Boiler Fault Codes Explained, Brand by Brand
Fault codes differ by manufacturer, but the same handful of problems show up again and again: low pressure, a flame that won't light or won't stay lit, a frozen condensate pipe, and a fan or sensor fault.
Quick answer
Fault codes differ by manufacturer, but the same handful of problems show up again and again: low pressure, a flame that won't light or won't stay lit, a frozen condensate pipe, and a fan or sensor fault. Low pressure and an accessible frozen condensate pipe are the only two things worth trying yourself. Anything involving ignition, the gas valve, the flue or a repeating fault code needs a Gas Safe registered engineer.
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Before you look up the code
Jump to your boiler: Vaillant · Worcester Bosch · Baxi · Ideal · Glow-worm · Main · Potterton · Viessmann · Ferroli · Vokera · Biasi
Two checks solve a large share of callouts, whatever make of boiler you have.
- Pressure. Look at the gauge. Below 1 bar cold, top up via the filling loop to about 1.2–1.5 bar.
- Frozen condensate pipe. In cold weather, the white plastic pipe running outside can freeze and lock the boiler out. Pour warm — never boiling — water along it, then reset once.
If either fixes it, you're done. If the same code comes straight back, stop resetting and book an engineer — repeated resets on a genuine fault can wear ignition components faster and, on some faults, aren't safe to keep repeating.
These sections cover the fault codes we're asked about most often, cross-checked against manufacturer documentation and current engineer guidance. They're a starting point for understanding what your boiler is telling you, not a substitute for the fault-code sticker inside your own boiler's casing flap — always check that against your exact model, since the same code can mean something different on an older or newer range from the same manufacturer.
Vaillant fault codes
Vaillant (ecoTEC, ecoFIT, turboTEC) uses F-prefixed codes, shown as "F." followed by two digits.
| Code | What it means | Safe to try yourself? |
|---|---|---|
| F.22 | System water pressure too low | Yes — repressurise via the filling loop |
| F.28 | Ignition failure — boiler tried to light and couldn't | No — check gas supply and condensate pipe, then one reset only |
| F.29 | Flame lit successfully, then lost during operation | No — engineer diagnosis needed |
| F.75 | Pump or pressure sensor fault — boiler can't detect water movement | No — usually a stuck pump or faulty sensor |
| F.00 | The boiler has lost the signal from the central heating flow (outgoing) temperature sensor (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.000 on 2024-on ecoTEC plus.) | No — beyond one reset - if the code returns, book a Gas Safe engineer |
| F.01 | The boiler has lost the signal from the central heating return temperature sensor (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.001 on 2024-on ecoTEC plus.) | No — beyond one reset - if the code returns, book a Gas Safe engineer |
| F.10 | The flow temperature sensor circuit has short-circuited (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.010 on 2024-on ecoTEC plus.) | No — beyond one reset - if the code returns, book a Gas Safe engineer |
| F.11 | The return temperature sensor circuit has short-circuited (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.011 on 2024-on ecoTEC plus.) | No — beyond one reset - if the code returns, book a Gas Safe engineer |
| F.20 | The safety cut-out has closed the gas valve because the flow or return sensor read above the maximum permitted temperature (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.020 on 2024-on ecoTEC plus.) | With the boiler off and the system cold, check the pressure gauge and top up via the filling loop to 1-1.5 bar if it reads below about 1 bar, then try one reset only. If the code returns, stop using the boiler and book a Gas Safe engineer |
| F.23 | Safety shutdown because the temperature difference between flow and return is too great (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.023 on 2024-on ecoTEC plus.) | With the boiler off and the system cold, check the pressure gauge and top up to 1-1.5 bar if low, then try one reset only. If the code returns, book a Gas Safe engineer |
| F.24 | Safety shutdown because the water temperature rose too quickly (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.024 on 2024-on ecoTEC plus.) | With the boiler off and the system cold, check the pressure gauge and top up to 1-1.5 bar if low, then try one reset only. If the code returns, book a Gas Safe engineer |
| F.25 | Safety shutdown because the flue gas temperature is too high (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.025 on 2024-on ecoTEC plus.) | This is a flue and combustion concern - stop using the boiler, do not keep resetting it and book a Gas Safe engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999 |
| F.26 | The gas valve is not operating - the boiler cannot control the gas supply to the burner (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3.) | This is a gas control fault - stop using the boiler and book a Gas Safe engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999 |
| F.27 | Safety shutdown because a flame signal is being detected while the burner should be off (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.027 on 2024-on ecoTEC plus.) | This can mean gas is passing when it should not - stop using the boiler, do not reset it and book a Gas Safe engineer immediately. If you smell gas, call the National Gas Emergency Service on 0800 111 999 |
| F.32 | The fan speed is outside tolerance, or the fan is not connected (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.032 on 2024-on ecoTEC plus.) | The fan is part of the combustion system - stop using the boiler and book a Gas Safe engineer |
| F.35 | The air intake or flue pipe is blocked (Documented as F.035 in the 2024-on ecoTEC plus manual; shown as F.35 on earlier ecoTEC plus models.) | This is a flue concern and must never be cleared by the householder - stop using the boiler and book a Gas Safe engineer. If you smell gas, call 0800 111 999 |
| F.42 | The coding resistor that tells the boiler its output and gas group is invalid or short-circuited (ecoTEC plus VU/VUW ..6/5-5. Shown as F.042 on 2024-on ecoTEC plus.) | No — book a Gas Safe engineer |
| F.49 | A fault on the eBUS wiring that links the boiler to its controls (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.049 on 2024-on ecoTEC plus.) | Check your thermostat or programmer has power and working batteries and is calling for heat, then try one reset. If the code returns, book a Gas Safe engineer |
| F.54 | The boiler failed to start because there is no gas inlet pressure or the inlet pressure is insufficient (ecoTEC plus VU/VUW ..6/5-5.) | Check the gas is on and that another gas appliance in the house works. Do not keep resetting - book a Gas Safe engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999 |
| F.56 | Safety shutdown after the boiler's carbon monoxide limit value was exceeded (ecoTEC plus VU/VUW ..6/5-5 fitted with the all-gas/CO sensor. Some other ecoTEC series document F.56 differently - check the manual for the exact model.) | Stop using the boiler immediately, do not reset it, and book a Gas Safe engineer. If anyone feels unwell or a CO alarm sounds, get everyone into fresh air and call the National Gas Emergency Service on 0800 111 999 |
| F.61 | The boiler cannot drive the gas valve assembly (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.061 on 2024-on ecoTEC plus.) | This is a gas control fault - stop using the boiler and book a Gas Safe engineer. If you smell gas, call 0800 111 999 |
| F.62 | The gas valve shut off later than it should have after the flame went out (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.062 on 2024-on ecoTEC plus.) | A delayed gas valve shut-off is a gas safety concern - stop using the boiler and book a Gas Safe engineer. If you smell gas, call 0800 111 999 |
| F.63 | The boiler's EEPROM memory has failed its read/write test (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.063 on 2024-on ecoTEC plus.) | No — beyond one reset - if the code returns, book a Gas Safe engineer |
| F.64 | A fault in the electronics or a safety-relevant sensor (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.064 on 2024-on ecoTEC plus.) | No — beyond one reset - if the code returns, book a Gas Safe engineer |
| F.65 | The electronics have exceeded their permitted operating temperature (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.065 on 2024-on ecoTEC plus.) | Make sure nothing is stacked tightly around the outside of the boiler restricting air movement, then try one reset. If the code returns, book a Gas Safe engineer |
| F.67 | The flame monitor is returning an implausible flame signal (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.067 on 2024-on ecoTEC plus.) | Flame detection is a safety control - stop using the boiler and book a Gas Safe engineer |
| F.68 | The flame monitor is reporting an unstable flame signal (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.068 on 2024-on ecoTEC plus.) | An unstable flame is a combustion concern - stop using the boiler and book a Gas Safe engineer. If you smell gas, call 0800 111 999 |
| F.70 | The Device Specific Number is missing, wrong, or does not match the coding resistor (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.070 on 2024-on ecoTEC plus.) | No — book a Gas Safe engineer |
| F.71 | The flow temperature sensor is returning implausible readings (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.071 on 2024-on ecoTEC plus.) | No — beyond one reset - if the code returns, book a Gas Safe engineer |
| F.72 | The temperature difference between the flow and return sensors is invalid (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.072 on 2024-on ecoTEC plus.) | No — beyond one reset - if the code returns, book a Gas Safe engineer |
| F.73 | The water pressure sensor signal is too weak - it is reporting that system pressure is too low (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3.) | With the boiler off and the system cold, check the pressure gauge and top up via the filling loop to 1-1.5 bar if it reads low, then try one reset. If the code returns, book a Gas Safe engineer |
| F.74 | The water pressure sensor signal is too strong - system pressure is too high or the sensor cable has short-circuited (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.074 on 2024-on ecoTEC plus.) | No — do not attempt to drain the system yourself. Book a Gas Safe engineer |
| F.76 | The overheating protection on the primary heat exchanger has operated (Documented as F.076 in the 2024-on ecoTEC plus manual; shown as F.76 on earlier ecoTEC plus models.) | Check pressure and top up if low, then try one reset - but this fault usually needs an engineer, as the protection device may have permanently operated |
| F.77 | A condensate pump or an external flue non-return flap is blocking burner operation (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.077 on 2024-on ecoTEC plus.) | This involves a flue safety device - stop using the boiler and book a Gas Safe engineer |
| F.78 | The hot water outlet sensor connection at an external control is interrupted (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.078 on 2024-on ecoTEC plus.) | No — book a Gas Safe engineer. The manual notes the boiler itself has usually not malfunctioned |
| F.83 | When the burner starts, the flow or return sensor registers no temperature rise, or the rise is too slow (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.083 on 2024-on ecoTEC plus.) | With the boiler off and the system cold, check the pressure gauge and top up to 1-1.5 bar if low, then try one reset. If the code returns, book a Gas Safe engineer |
| F.84 | The temperature difference between the flow and return sensors is implausible (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.084 on 2024-on ecoTEC plus.) | No — book a Gas Safe engineer |
| F.85 | The flow and return temperature sensors have been fitted incorrectly (ecoTEC plus VU/VUW ..6/5-5, ecoTEC pro VUW ..6/5-3. Shown as F.085 on 2024-on ecoTEC plus.) | No — book a Gas Safe engineer |
| F.92 | The coding resistor on the PCB does not match the gas group entered in the boiler (ecoTEC plus VU/VUW ..6/5-5. Shown as F.092 on 2024-on ecoTEC plus, where it indicates an incomplete gas-type conversion.) | This concerns the gas setting of the appliance - stop using the boiler and book a Gas Safe engineer. If you smell gas, call 0800 111 999 |
| F.93 | The boiler has detected combustion quality outside the permitted range and is asking for the gas route to be checked (ecoTEC plus VU/VUW ..6/5-5.) | This is a combustion concern - stop using the boiler and book a Gas Safe engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999 |
Worcester Bosch fault codes
Worcester Bosch Greenstar models show a fault code paired with a cause code — for example "EA" with "227" — and it's the pair together that identifies the problem.
| Code | What it means | Safe to try yourself? |
|---|---|---|
| EA 227 | No flame detected after ignition | Often a frozen condensate pipe — thaw and reset once |
| EA 229 | Flame was lit, then lost during operation | No — engineer diagnosis needed |
| E9 224 | Flue or high-limit thermostat activated (overheat) | No — flue and fan need inspecting |
| A1 281 | Pump stuck or running dry | No — check pressure first, then engineer |
| EA 261 | The heat control module (HCM/code plug) or burner control unit is suspected defective or badly seated (Meaning differs by series - see notes. Greenstar i ErP: 'HCM potentially defective'. CDi Compact ErP: 'Ignition timing error'.) | No — book a Gas Safe registered engineer. You may press reset once, but if the code returns do not reset again. If you smell gas, call 0800 111 999 |
| E9 219 | The safety sensor on the main heat exchanger has recorded a temperature above its 105 degrees C limit and locked the boiler out (Greenstar CDi Compact ErP.) | Check the pressure gauge and, if it is below the normal band, top the system up using the filling loop, then press reset ONCE. If the code returns, stop using the boiler and book a Gas Safe registered engineer |
| E9 220 / E9 221 | The maximum temperature (safety) sensor on the main heat exchanger has short circuited (220) or is not being recognised/open circuit (221) (Greenstar CDi Compact ErP.) | No — book a Gas Safe registered engineer |
| E9 276 | The primary flow temperature has exceeded 95 degrees C, so the boiler has blocked and is waiting for it to cool (Greenstar i ErP and CDi Compact ErP.) | Check the pressure gauge and top up via the filling loop if it is low, then allow the boiler to cool. You may press reset ONCE. If it recurs, book a Gas Safe registered engineer |
| E9 277 | The main heat exchanger safety sensor has exceeded 95 degrees C; the boiler pauses and will lock out with error 219 if the temperature does not fall (Greenstar CDi Compact ErP.) | Check the pressure gauge and top up via the filling loop if low. If the fault persists, book a Gas Safe registered engineer |
| E9 285 | The return temperature has exceeded 95 degrees C; the boiler stops the burn and will lock out with error 286 if the temperature keeps rising (Greenstar CDi Compact ErP.) | Check the pressure gauge and top up via the filling loop if low. If the fault persists, book a Gas Safe registered engineer |
| E5 218 | The primary flow temperature has risen too high and the flow sensor has registered an overheat (Greenstar CDi Compact ErP.) | Check the pressure gauge and top up via the filling loop if low, then press reset ONCE. If it returns, book a Gas Safe registered engineer |
| E5 332 | The primary flow sensor has recorded a temperature above 110 degrees C (Greenstar CDi Compact ErP.) | No — beyond checking the pressure gauge and topping up via the filling loop if it is low - book a Gas Safe registered engineer |
| E2 222 | The flow temperature sensor circuit is reading as short circuited (Greenstar i ErP and CDi Compact ErP. Greenstar i ErP also lists E2 350 for the same condition.) | No — book a Gas Safe registered engineer |
| E2 223 | The flow temperature sensor is reading as disconnected or open circuit (Greenstar i ErP and CDi Compact ErP. Greenstar i ErP also lists E2 351 for the same condition.) | No — book a Gas Safe registered engineer |
| C6 215 | The fan is running faster than the control board expects (Greenstar i ErP and CDi Compact ErP. Greenstar 4000/8000 show 215 alone.) | No — book a Gas Safe registered engineer |
| C6 216 | The fan is running slower than the control board expects (Greenstar i ErP and CDi Compact ErP. Greenstar 4000/8000 show 216 alone.) | No — book a Gas Safe registered engineer |
| C7 214 | The fan did not run during the boiler's start-up phase, so it has shut down within the safety time (Greenstar i ErP and CDi Compact ErP. Greenstar 4000/8000 show 214 alone ('Fan shut down during safety time').) | No — book a Gas Safe registered engineer |
| C7 217 | The fan stopped, or no airflow was detected, while the boiler was running (Greenstar i ErP and CDi Compact ErP.) | No — book a Gas Safe registered engineer. This can indicate a blocked flue, so do not keep resetting the boiler |
| C1 264 | Airflow stopped while the boiler was operating (a blocking fault, so it will restart itself if the condition clears) (Greenstar i ErP and CDi Compact ErP.) | No — book a Gas Safe registered engineer, as this can indicate a flue problem |
| C4 273 | The boiler briefly interrupts itself (up to about 2 minutes) for a safety check after 24 hours of continuous running, then resumes on its own (Greenstar i ErP and CDi Compact ErP.) | Check whether the heating or hot water has been calling constantly for 24 hours; the boiler blocks for a minimum of about 2 minutes and then resumes on its own. If it does not, book a Gas Safe registered engineer |
| D1 240 | The return temperature sensor circuit is reading as short circuited (Greenstar CDi Compact ErP.) | No — book a Gas Safe registered engineer |
| D1 241 | The return temperature sensor is reading as disconnected (Greenstar CDi Compact ErP.) | No — book a Gas Safe registered engineer |
| D1 286 | The return temperature is too high and the boiler has locked out on overheat (Greenstar CDi Compact ErP.) | Check the pressure gauge and top up via the filling loop if it is low. If the code returns, book a Gas Safe registered engineer |
| D4 271 | The temperature difference between the primary flow sensor and the safety sensor is greater than the permitted limit (they should be within 15 degrees C of each other) (Greenstar CDi Compact ErP. Greenstar i ErP lists D4 341 'Primary flow temperatures rising too fast'.) | No — book a Gas Safe registered engineer |
| A7 808 | The domestic hot water temperature sensor is faulty (Greenstar i ErP. CDi Compact/Greenstar 8000 use 1022 for cylinder sensor faults.) | No — book a Gas Safe registered engineer. Heating may still work while hot water is affected |
| 9U 233 | The heat control module (the boiler's code plug) is loose or defective, or the control box has failed (Greenstar i ErP and CDi Compact ErP. Greenstar 4000/8000 show 233 ('Boiler identification module or device electronics faulty').) | No — book a Gas Safe registered engineer |
| b7 257 | An internal fault has been detected in the control board or heat control module (Greenstar i ErP and CDi Compact ErP.) | No — book a Gas Safe registered engineer |
| F7 228 | A flame (ionisation) signal was detected before the burner was due to start - a false flame reading (Greenstar i ErP and CDi Compact ErP. Greenstar 4000/8000 show 228 ('Flame signal without flame present').) | No — stop using the boiler and book a Gas Safe registered engineer. This is a flame-detection safety fault, so do not keep resetting. If you smell gas, call 0800 111 999 |
| FA 306 | A flame signal is still being detected after the gas valve has closed (Greenstar i ErP, CDi Compact ErP and Greenstar 8000 (as 306).) | Stop using the boiler and call a Gas Safe registered engineer straight away - this fault can indicate a gas valve passing gas. If you smell gas, turn the gas off at the meter if it is safe to do so, do not use switches or naked flames, ventilate the room and call the National Gas Emergency Service on 0800 111 999 |
| FA 364 | The gas valve EV2 leak test has failed, indicating the second gas valve seat is not sealing (Greenstar CDi Compact ErP.) | Stop using the boiler and call a Gas Safe registered engineer immediately - this is a gas valve leak test failure. If you smell gas, turn the gas off at the meter if it is safe, avoid switches and naked flames, ventilate and call 0800 111 999 |
| Fb 365 | The gas valve EV1 leak test has failed, indicating the first gas valve seat is not sealing (Greenstar CDi Compact ErP.) | Stop using the boiler and call a Gas Safe registered engineer immediately - this is a gas valve leak test failure. If you smell gas, turn the gas off at the meter if it is safe, avoid switches and naked flames, ventilate and call 0800 111 999 |
| F0 238 | A gas valve or control box error has been detected (Greenstar i ErP. Greenstar 4000/8000 show 234 ('Gas valve electrical fault') and 238 ('Boiler electronics faulty').) | No — book a Gas Safe registered engineer. Do not keep resetting |
| Fd 231 | The mains electrical supply was interrupted while the boiler was in a lockout condition (Greenstar i ErP and CDi Compact ErP. Cause code 226 in the same group indicates a service tool has been connected.) | Check the boiler's fused spur and consumer unit are on, then press reset ONCE. Importantly, this code hides an earlier lockout - if the boiler will not run afterwards, book a Gas Safe registered engineer to read the fault history rather than resetting repeatedly |
| EF 349 | The boiler is detecting near-boil conditions in the central heating - a large flow-to-return temperature difference of more than 18 degrees C even at minimum burner output (Greenstar CDi Compact ErP.) | Check the pressure gauge and top up via the filling loop if it is low, and check that radiator valves and any system valves are open. If the code persists, book a Gas Safe registered engineer |
| CC 800 | The outdoor weather compensation sensor is faulty (only relevant when the optional outdoor sensor accessory is fitted) (Greenstar i ErP (also listed as H29 in the maintenance menu). Greenstar 8000 uses 1037/1068.) | No — book a Gas Safe registered engineer. The boiler will normally continue to heat, but weather compensation will not work correctly |
| H09 | Communication between the boiler and its modulating pump has failed (Greenstar i ErP maintenance menu. Greenstar 8000 shows 1019 ('Incorrect pump type detected').) | No — book a Gas Safe registered engineer |
| H11 | The domestic hot water flow/temperature sensor is faulty (Greenstar i ErP maintenance menu.) | No — book a Gas Safe registered engineer |
| H03 / H08 / H13 | A service reminder - the set burner hours (H03), the set service date (H08), or the maximum service interval in months (H13) has been reached (Greenstar i ErP maintenance menu. Greenstar 8000 uses 1018 and 1070/1071/1072 for the equivalent reminders.) | This is a service reminder, not a breakdown - book your annual boiler service with a Gas Safe registered engineer. The boiler will normally keep running |
| 1017 | The system water pressure is too low (Greenstar 4000 and 8000 range (numeric code family).) | Top the system up using the filling loop until the gauge reads within the normal band shown in your user guide (typically around 1 to 1.5 bar when cold), then close both filling loop valves. If the pressure keeps dropping, you have a leak - book a Gas Safe registered engineer |
| 1065 | The system pressure sensor is faulty or is not connected (Greenstar 4000 and 8000 range.) | No — book a Gas Safe registered engineer |
Baxi fault codes
Baxi (Duo-tec, Platinum+, Megaflo System) uses three-digit E-codes. The exact set varies a little by range, so check the label inside the casing flap for your specific model.
| Code | What it means | Safe to try yourself? |
|---|---|---|
| E119 | Low system water pressure | Yes — repressurise via the filling loop |
| E133 | Ignition or gas supply fault | Check gas supply and condensate pipe, then one reset |
| E125 | Circulation fault — poor water movement round the system | No — often pump, airlock or blockage |
| E168 | General fault, often after a power interruption | Worth one reset — call an engineer if it returns |
| E110 | Overheat lockout - primary flow temperature exceeded the safe limit or the safety (overheat) thermostat has tripped (Duo-tec Combi, Duo-tec Compact Combi, Baxi 600/800 Combi & System, Platinum, EcoBlue, Assure) | Check the pressure gauge reads about 1-1.5 bar when the system is cold and top up via the filling loop if it is low, and make sure radiator valves are open. Then try ONE reset. If E110 comes back, stop using the boiler and book a Gas Safe engineer - repeated resetting on an overheat lockout is not safe |
| E09 | Gas valve connection fault - a wiring or connection problem on the gas valve circuit (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | No — book a Gas Safe engineer |
| E15 | Gas valve command fault - the PCB cannot correctly drive or verify the gas valve (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | No — book a Gas Safe engineer |
| E20 | Central heating (flow) NTC sensor fault - open circuit or short circuit (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | No — book a Gas Safe engineer |
| E28 | Flue gas NTC sensor fault - open circuit or short circuit (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | If the plastic condensate pipe running outside is frozen, thaw it with warm - not boiling - water, then try ONE reset. Otherwise stop using the boiler and book a Gas Safe engineer; do not keep resetting |
| E40 | Central heating return NTC sensor fault - open circuit or short circuit (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | No — book a Gas Safe engineer |
| E50 | Domestic hot water cylinder NTC sensor fault - open circuit or short circuit (Duo-tec, Duo-tec Compact, 600/800 System, Megaflo System, Assure System (storage/tank models)) | No — book a Gas Safe engineer |
| E83/E84/E85/E86/E87 | No communication between the boiler and its room controller or interface board (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | Check the room thermostat or programmer batteries and that it is switched on and calling for heat. Nothing further is safe - book a Gas Safe engineer if the code stays |
| E103 | The Safety Assist battery is exhausted (Models fitted with Baxi Safety Assist) | No — book a Gas Safe engineer |
| E104 | Faulty Safety Assist PCB (Models fitted with Baxi Safety Assist) | Stop using the boiler and book a Gas Safe engineer - this fault relates to a carbon monoxide safety device. If you smell gas or feel unwell, leave the property and call 0800 111 999 |
| E109 | Pre-circulation fault - the boiler could not establish flow before firing (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | Check the pressure gauge reads about 1-1.5 bar cold and top up via the filling loop if low, and make sure radiator and system valves are open. Then try ONE reset. If it returns, book a Gas Safe engineer |
| E118 | System water pressure is too low (below approximately 0.5 bar) (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | Top the system up using the filling loop until the gauge reads 1-1.5 bar with the heating cold, then close the filling loop valves firmly. If the pressure keeps dropping you have a leak - book an engineer |
| E128 | Safety lockout after repeated loss of flame during normal operation (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | Check your other gas appliances work and, if the outside condensate pipe is frozen, thaw it with warm - not boiling - water. Then try ONE reset. If E128 returns, stop using the boiler and book a Gas Safe engineer; do not keep resetting. If you smell gas, leave and call 0800 111 999 |
| E129 | Safety lockout for repeated flame loss with maximum correction applied during the calibration function (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | Stop using the boiler and book a Gas Safe engineer. If you smell gas, leave the property and call the National Gas Emergency Service on 0800 111 999 |
| E130 | Flue gas overheat lockout - the flue thermostat or flue NTC has operated (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | Stop using the boiler and book a Gas Safe engineer - this is a flue and combustion fault. Do not reset it repeatedly. If you smell gas or feel unwell, leave the property and call 0800 111 999 |
| E134 | The gas valve was open for the allowed time without gas being present (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | Check that other gas appliances in the property work, so the gas supply is on. Then try ONE reset. If it returns, stop using the boiler and book a Gas Safe engineer. If you smell gas, leave and call 0800 111 999 |
| E135 | Internal error, listed in Baxi manuals alongside the gas supply interruption faults (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | Try ONE reset. If it returns, stop using the boiler and book a Gas Safe engineer - do not keep resetting |
| E154 | Flow and return sensor plausibility test failed - the two readings do not make sense together (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | No — book a Gas Safe engineer |
| E160 | Fan fault - the fan is not running, not reaching the required speed, or its wiring has failed (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | Stop using the boiler and book a Gas Safe engineer - the fan is part of the flue and combustion system |
| E270 | Dry fire - the boiler fired with little or no water in the primary heat exchanger (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | Stop using the boiler and book a Gas Safe engineer. Do not repeatedly reset it - firing dry can damage the heat exchanger |
| E321 / 163 | Domestic hot water NTC sensor fault - open circuit or short circuit (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | No — book a Gas Safe engineer |
| E384 / 164 | False or parasitic flame - the control detects a flame signal when there should be none (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | Stop using the boiler and book a Gas Safe engineer - this is a gas and combustion safety fault. If you smell gas, leave the property and call 0800 111 999 |
| E385 / 165 | Under voltage - the mains supply to the boiler is too low (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | No — book a Gas Safe engineer, who may recommend an electrician |
| E430 / 166 | Temporary water pressure fault, or the water pressure test has failed (shown with a crossed flame symbol) (Duo-tec, Duo-tec Compact, 600/800 Combi & System, Platinum, EcoBlue, Assure) | Check the gauge and, if below about 1 bar, top up via the filling loop to 1-1.5 bar with the heating cold, then close the loop valves. If it keeps dropping there is a leak - book an engineer |
| A.02.06 | Low water pressure in the heating circuit (warning - the boiler may still run) (Baxi 600/800 Combi 2, 600/800 System 2, Assure 500 Combi 2 / System 2) | Top the system up using the filling loop until the gauge reads 1-1.5 bar with the heating cold, then close the filling loop valves firmly. If it keeps dropping there is a leak - book an engineer |
| H.02.07 | Low pressure in the heating circuit, present continuously (Baxi 600/800 Combi 2, 600/800 System 2, Assure 500 Combi 2 / System 2) | Top the system up via the filling loop to 1-1.5 bar with the heating cold and close the loop valves. If the pressure falls again there is a leak - book an engineer |
| E.04.10 | Ignition lockout - the burner failed to ignite after 4 attempts (Baxi 600/800 Combi 2, 600/800 System 2, Assure 500 Combi 2 / System 2) | Check your other gas appliances work and, if the outside condensate pipe is frozen, thaw it with warm - not boiling - water. Then try ONE reset. If it returns, stop using the boiler and book a Gas Safe engineer; do not keep resetting. If you smell gas, leave and call 0800 111 999 |
| E.01.04 | Lockout after flame loss was detected five times within 24 hours with the burner on (Baxi 600/800 Combi 2, 600/800 System 2, Assure 500 Combi 2 / System 2) | Check other gas appliances work, and thaw the external condensate pipe with warm - not boiling - water if it is frozen. Then try ONE reset. If it returns, stop using the boiler and book a Gas Safe engineer |
| H.03.02 | Temporary flame loss - the flame was lost but the boiler has not locked out (Baxi 600/800 Combi 2, 600/800 System 2, Assure 500 Combi 2 / System 2) | Check other gas appliances work, and thaw the external condensate pipe with warm - not boiling - water if it is frozen. If the fault recurs, book a Gas Safe engineer |
| E.04.13 | Fan impeller blocked, or the maximum fan speed was exceeded (Baxi 600/800 Combi 2, 600/800 System 2, Assure 500 Combi 2 / System 2) | Stop using the boiler and book a Gas Safe engineer - the fan is part of the flue and combustion system |
| E.04.08 | Maximum safe temperature reached - the overheat protection has operated (Baxi 600/800 Combi 2, 600/800 System 2, Assure 500 Combi 2 / System 2) | Check the pressure is about 1-1.5 bar cold and top up via the filling loop if low, and open radiator valves. Then try ONE reset. If it returns, stop using the boiler and book a Gas Safe engineer |
| E.01.17 | No water circulation - permanent lockout requiring reset (Baxi 600/800 Combi 2, 600/800 System 2, Assure 500 Combi 2 / System 2) | Check the pressure is about 1-1.5 bar cold and top up via the filling loop if low, and make sure radiator valves are open. Then try ONE reset. If it returns, book a Gas Safe engineer |
| E.01.20 | Maximum flue gas temperature reached (Baxi 600/800 Combi 2, 600/800 System 2, Assure 500 Combi 2 / System 2) | Stop using the boiler and book a Gas Safe engineer - this is a flue and combustion fault |
| E.02.17 | Permanent communication failure between the gas valve and the boiler PCB (Baxi 600/800 Combi 2, 600/800 System 2, Assure 500 Combi 2 / System 2) | Stop using the boiler and book a Gas Safe engineer |
Ideal fault codes
Ideal (Logic, Logic+, Vogue) mixes F- and L-prefixed codes depending on the model and control board fitted.
| Code | What it means | Safe to try yourself? |
|---|---|---|
| F1 | Low system water pressure | Yes — repressurise via the filling loop |
| L2 / F2 | Ignition lockout — flame lost or never established | Check gas supply and condensate pipe, then one reset |
| F3 | Fan fault | No — engineer diagnosis needed |
| L9 / F9 | PCB (control board) fault | No — engineer diagnosis needed |
| L5 | Five or more resets within about 15 minutes — a safety trip, not a new fault | No — find and fix what's actually triggering it (usually F1 or L2) |
| L1 | Flow temperature overheat lockout, or no water flow lockout - the boiler has shut down because the water leaving it got too hot or is not moving (Logic / Logic+ / Logic Max (Combi, System, Heat). Vogue shows this as the words "Overheat Lockout".) | Check the pressure gauge reads between 1 and 1.5 bar when the boiler is cold and top up with the filling loop if it is low, and check the radiator valves and any system isolation valves are open. You may press reset ONCE. If it locks out again, stop and book a Gas Safe engineer - do not keep resetting |
| L2 | Ignition lockout - the boiler has tried to light and failed, so it has locked itself out on a safety shutdown (Logic / Logic+ / Logic Max. Vogue shows "Ignition Lockout".) | If you can smell gas at any time, leave the property and call the National Gas Emergency Service on 0800 111 999 immediately. Otherwise check other gas appliances still work, check the gas is on at the meter and any prepayment meter has credit, and if an outside condensate pipe is frozen pour warm (never boiling) water over it. You may press reset ONCE. If it locks out again, stop using the boiler and book a Gas Safe engineer - repeated resetting is dangerous |
| LC | Five resets/restarts have been made within 15 minutes, so the boiler has stopped accepting further resets (Logic / Logic+ / Logic Max. Vogue shows "Too Many Resets".) | No — book a Gas Safe engineer. Do not press reset again; this code means a real fault has already been reset five times and needs diagnosing |
| L6 | False flame lockout - the boiler is detecting a flame signal when there should be no flame present (Logic / Logic+ / Logic Max. Vogue shows "Flame On Before Gas Valve On".) | No — book a Gas Safe engineer. Do not attempt to reset repeatedly |
| L7 | The boiler has failed to achieve a 5C temperature rise on three successive firing attempts (Logic Max Heat (heat-only) and related heat/system models.) | Check the pressure gauge reads 1 to 1.5 bar cold and top up with the filling loop if low, and check radiator valves are open. Otherwise book a Gas Safe engineer |
| F2 / Fn / Ln | Flame loss - the burner lit but the flame was then lost during operation (Logic / Logic+ / Logic Max (the letter shown varies with PCB version). Vogue shows "Flame Loss".) | If you can smell gas at any time, leave the property and call the National Gas Emergency Service on 0800 111 999. Otherwise check other gas appliances work, check the gas is on at the meter and any prepayment meter has credit, and thaw an outside condensate pipe with warm (not boiling) water if it is frozen. You may press reset ONCE, then book a Gas Safe engineer if it returns |
| F4 / L4 | Flow thermistor fault - the sensor measuring the water leaving the boiler is out of range or open/short circuit (Logic / Logic+ / Logic Max (Logic Max Heat calls it the control/no flow thermistor). Vogue shows "Flow Thermistor Fault".) | You may press reset ONCE. If the code returns, book a Gas Safe engineer - there is nothing safe for you to check inside the boiler |
| F5 / L5 | Return thermistor fault - the sensor measuring the water returning to the boiler is out of range or open/short circuit. On most Logic models this is the return thermistor; on some Ideal models L5 instead means the boiler has been reset too many times in 15 minutes - if L5 appears after repeated resets, stop and book an engineer (Logic / Logic+ / Logic Max. Vogue shows "Return Thermistor Fault".) | You may press reset ONCE. If the code returns, book a Gas Safe engineer |
| F6 | Outside sensor fault - the external weather-compensation sensor is not reading correctly (Logic / Logic+ / Logic Max. Vogue shows "Outside Sensor Fault".) | No — book a Gas Safe engineer. Heating will usually still work, but weather compensation will be lost |
| F7 | Low mains voltage - the electrical supply reaching the boiler is below the minimum it needs (Logic / Logic+ / Logic Max. Vogue shows "Low Mains Voltage" (below 185V).) | Check whether other electrical items in the house are affected and contact your electricity provider or a qualified electrician. Do not open the boiler or touch any wiring yourself |
| F9 / L9 / F8 / L8 | Unconfigured or faulty printed circuit board, or a gas valve short circuit pulling the board into fault (Logic Combi ESP1 and Logic Max Combi C series - unconfigured/faulty PCB. IMPORTANT: on Logic Max Heat (heat-only) manuals this same group of codes instead indicates a flow/return differential greater than 50C. Vogue shows "PCB Fault".) | No — book a Gas Safe engineer. The control board is the boiler's brain and must not be touched by anyone unqualified |
| FA | The boiler is seeing the return hotter than the flow, indicating reversed flow/return pipework or a flow/return thermistor fault (Logic Combi ESP1 / Logic Max Combi C - negative differential, flow or return thermistor fault. On Logic Max Heat and per Ideal's own FAQ - flow and return connections reversed.) | No — book a Gas Safe engineer. This normally points to how the pipework or sensors were fitted |
| Fd | No water flow - the boiler cannot detect water circulating through it (Logic Max Heat / heat-only and system models. Vogue shows "No Water Flow Fault".) | Check the pressure gauge reads 1 to 1.5 bar cold and top up with the filling loop if low, and check radiator and system isolation valves are open. If the code stays, book a Gas Safe engineer |
| FU | Excessive flow-to-return temperature difference (greater than 50C) across the boiler (Logic Combi ESP1 / Logic Max Combi C - flow/return differential greater than 50C. On Logic Max Heat (heat-only) - PCB unconfigured/faulty or gas valve short circuit.) | Check radiator valves and system isolation valves are open and that the pressure reads 1 to 1.5 bar cold, topping up with the filling loop if low. If the code stays, book a Gas Safe engineer |
| dU | The diverter valve has been left in its mid (service) position, so the boiler will not run normally (Logic Combi ESP1 / Logic Max Combi C series.) | Rotate the boiler control knobs fully clockwise, then switch the boiler's electrical supply off and back on and press restart once. If the code stays, book a Gas Safe engineer |
| L3 | No water flow - the boiler cannot detect circulation (Listed on Ideal Heating's official fault code FAQ index for Logic-family boilers.) | Check the pressure gauge reads 1 to 1.5 bar cold and top up with the filling loop if low, and check radiator and isolation valves are open. You may press reset ONCE, then book a Gas Safe engineer if it returns |
| F0 | No water flow thermistor - the flow-sensing thermistor is not being seen by the control board (Listed on Ideal Heating's official fault code FAQ index.) | No — book a Gas Safe engineer |
| C0 | BCC activation fault - the boiler configuration chip has not activated the control board correctly (Logic-family boilers with a BCC (Boiler Configuration Chip). Listed on Ideal Heating's official fault code FAQ index.) | No — book a Gas Safe engineer |
| C2 | BCC chip fault - the boiler configuration chip is missing, incorrect or unreadable (Logic-family boilers with a BCC chip. Listed on Ideal Heating's official fault code FAQ index.) | No — book a Gas Safe engineer |
| Thermal Fuse Lockout (text message) | A thermal fuse or overheat safety device has operated and shut the boiler down (Vogue / Vogue Gen2 / Vogue Max - these boilers display words, not letter codes.) | No — stop using the boiler and book a Gas Safe engineer. Do not attempt to reset it repeatedly |
| Flame On Before GV On (text message) | A flame signal was detected before the gas valve was opened - the Vogue equivalent of a false flame lockout (Vogue / Vogue Gen2 / Vogue Max.) | No — book a Gas Safe engineer |
| PCB Replaced (text message) | A new control board has been fitted but has not yet been configured to the appliance (Vogue / Vogue Gen2 / Vogue Max.) | No — book a Gas Safe engineer to complete the configuration |
| Pump Rotor Blocked (text message) | The pump rotor is jammed and cannot turn (Vogue / Vogue Gen2 / Vogue Max.) | No — book a Gas Safe engineer |
| No Connection to Primary PCB (text message) | The user interface board has lost communication with the boiler's primary control board (Vogue / Vogue Gen2 / Vogue Max.) | No — book a Gas Safe engineer |
| Pump Low Voltage Fault (text message) | The pump is not receiving the voltage it needs to run correctly (Vogue / Vogue Gen2 / Vogue Max.) | No — book a Gas Safe engineer. If other electrics in the house are also affected, contact your electricity provider |
| Flow/Return Reversed (text message) | The boiler is seeing the flow and return the wrong way round (Vogue / Vogue Gen2 / Vogue Max. Equivalent to 'FA' on Logic Max Heat.) | No — book a Gas Safe engineer |
| C | The boiler is running on a central heating demand (Logic / Logic+ / Logic Max. Status code, not a fault.) | No action needed - this is normal operation |
| D | The boiler is running on a hot water demand (Logic / Logic+ / Logic Max. Status code, not a fault.) | No action needed - this is normal operation |
| 0 / 00 | The boiler is on standby, waiting for a heating or hot water demand (Logic / Logic+ / Logic Max. Status code, not a fault.) | No action needed. If you expected heating, check the programmer and room thermostat are switched on and calling for heat, and check the thermostat batteries |
| PH | The boiler is running in domestic hot water preheat mode (Logic Max Combi. Status code, not a fault.) | No action needed - this is normal operation |
| FP | The boiler is running in frost protection mode (Logic Max Combi. Status code, not a fault.) | No action needed - this is normal operation and protects the boiler in cold weather |
| - - | The boiler mode knob is in the off position (Logic Max Combi. Status code, not a fault.) | Rotate the boiler mode knob fully clockwise to restore hot water and central heating operation |
Glow-worm fault codes
Glow-worm (part of the Vaillant Group) is the one manufacturer here where we'd urge real caution reading a generic table: fault codes vary more between its own ranges — Betacom, Flexicom, Ultracom — than they do for the other four manufacturers above. Betacom models don't show a code at all, just a coloured LED. The two codes below are consistent across most current ranges; for anything else, check your model's own label or manual rather than a general guide.
| Code | What it means | Safe to try yourself? |
|---|---|---|
| F22 | Low system water pressure | Yes — repressurise via the filling loop |
| F28 | Ignition fault, commonly a frozen condensate pipe | Check condensate pipe, thaw if frozen, then one reset |
| F.00 / F.01 | Open circuit on the flow (F.00) or return (F.01) temperature sensor, so the boiler cannot read water temperature (Energy, Energy7, Easicom 3, Betacom 3 (and shared Vaillant-platform ranges). F.00 = flow sensor, F.01 = return sensor) | No — book a Gas Safe engineer |
| F.10 / F.11 | Short circuit detected on the flow (F.10) or return (F.11) temperature sensor (Energy, Energy7, Easicom 3, Betacom 3. F.10 = flow sensor, F.11 = return sensor) | No — book a Gas Safe engineer |
| F.12 / F.91 | Short circuit on the cylinder temperature sensor (Energy7 (cylinder/store models). Not listed in the Easicom 3 or Betacom 3 tables) | No — book a Gas Safe engineer |
| F.13 | Short circuit on the temperature sensor for the domestic hot water cylinder (Energy, Energy7, Easicom 3, Betacom 3 (stored hot water systems)) | No — book a Gas Safe engineer |
| F.20 | Safety shutdown - the overheat temperature limit was reached and the boiler has locked out (Energy, Energy7, Easicom 3, Betacom 3) | Check the pressure gauge reads 1.0-1.5 bar when cold and top up via the filling loop if it is low. You may press reset ONCE. If it locks out again, stop using the boiler and call a Gas Safe engineer - do not keep resetting an overheat lockout |
| F.23 | Safety shutdown - the temperature difference between the flow and return sensors (NTC1/NTC2) is too great (Energy, Energy7, Easicom 3, Betacom 3) | Check the pressure gauge reads 1.0-1.5 bar cold and top up via the filling loop if low. You may press reset ONCE. If it returns, book a Gas Safe engineer |
| F.24 | Safety shutdown - the water temperature rose too quickly, indicating poor circulation (Energy, Energy7, Easicom 3, Betacom 3) | Check the pressure gauge reads 1.0-1.5 bar cold and top up via the filling loop if low. You may press reset ONCE. If it returns, book a Gas Safe engineer |
| F.25 | Safety shutdown - flue gas temperature too high, or a break in the flue gas safety cut-out circuit (Energy, Energy7, Easicom 3, Betacom 3) | This is a flue-related safety shutdown. Stop using the boiler and call a Gas Safe engineer. If you smell gas at any point, call the National Gas Emergency Service on 0800 111 999 |
| F.27 | Safety shutdown - a flame signal is detected when there should be none (Energy, Energy7, Easicom 3, Betacom 3) | Do not reset. Stop using the boiler and call a Gas Safe engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999 and turn off the gas at the meter (emergency control valve) if instructed |
| F.29 | Flame loss - the burner lit but the flame was lost during operation (Energy, Energy7, Easicom 3, Betacom 3) | Check your gas is on and other gas appliances work. If the external condensate pipe is frozen, thaw the outside pipe with warm - not boiling - water. Then press reset ONCE. If it recurs, stop and call a Gas Safe engineer. If you smell gas, call 0800 111 999 |
| F.32 | Fan speed is outside the tolerance values; the fan frost protection function is active (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer. This concerns the fan and flue system |
| F.33 | Air pressure switch fault - the pressure monitor has not switched, or switched at too high a fan speed, indicating insufficient air supply (Betacom 3 and the Glow-worm Energy range fault list. NOT listed in the Energy7 or Easicom 3 manuals, which have no air pressure switch) | This concerns the flue and air supply. Stop using the boiler and call a Gas Safe engineer. If you smell fumes or gas, call 0800 111 999 |
| F.49 | eBUS fault - the voltage on the eBUS control communication link is too low (Energy, Energy7, Easicom 3, Betacom 3) | Check your thermostat or programmer has good batteries and is calling for heat. Do not open the boiler or any wiring - book a Gas Safe engineer if the code stays |
| F.61 | Fault in the gas valve assembly control circuit (Energy, Energy7, Easicom 3, Betacom 3) | This is a gas valve fault. Do not reset repeatedly. Stop using the boiler and call a Gas Safe engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999 |
| F.62 | Gas valve switch-off control fault - the gas valve is switching off late or the flame signal is slow to extinguish (Energy, Energy7, Easicom 3, Betacom 3) | A leaking or slow-closing gas valve is a possible cause. Do not reset. Stop using the boiler and call a Gas Safe engineer. If you smell gas, call 0800 111 999 |
| F.63 | EEPROM fault - the PCB's stored configuration data is corrupt or unreadable (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer |
| F.64 | Fault in the electronics, sensor or analogue-to-digital converter circuit (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer |
| F.65 | Electronics temperature too high - the PCB itself is overheating (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer |
| F.67 | The flame signal value returned by the ASIC on the PCB is incorrect (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer |
| F.68 | Unstable flame signal on the analogue input (Energy, Energy7, Easicom 3, Betacom 3) | This is a combustion-related fault. Do not adjust anything. Stop using the boiler and call a Gas Safe engineer. If you smell gas, call 0800 111 999 |
| F.70 | Invalid product code - the boiler does not have a valid Device Specific Number (DSN) (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer |
| F.71 | The flow temperature sensor is reporting a constant, unchanging value (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer |
| F.72 | Deviation fault - the difference between the flow and return temperature sensor readings is too great (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer |
| F.73 | The water pressure sensor is not connected or has short-circuited (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer. Do not attempt to reach the sensor |
| F.74 | Electrical problem in the water pressure sensor circuit (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer |
| F.75 | Pressure sensor fault - the boiler does not see the expected pressure rise when the pump starts (Energy, Energy7, Easicom 3, Betacom 3 - the code Synergy has repaired. Note Betacom 3 lists the cause as pressure sensor or pump defective or low water pressure) | Check the pressure gauge reads 1.0-1.5 bar cold and top up via the filling loop if it is low, then press reset ONCE. If the code returns, stop and book a Gas Safe engineer - do not keep resetting |
| F.76 | The safety cut-out in the primary heat exchanger is defective (Energy7 / Energy. Not listed in the Easicom 3 or Betacom 3 tables) | This is a heat exchanger safety device fault. Stop using the boiler and call a Gas Safe engineer. Do not reset repeatedly |
| F.77 | Condensate or flue fault - no response from the condensate pump or the flue non-return flap (Energy, Energy7, Easicom 3, Betacom 3) | If the external condensate pipe is frozen, thaw the outside pipe with warm - not boiling - water, then press reset ONCE. Otherwise there is nothing safe to try - book a Gas Safe engineer. Do not touch the flue |
| F.78 | Interruption to the domestic hot water outlet sensor at the external control (Energy, Energy7, Easicom 3, Betacom 3 - UK installations using a link box) | No — book a Gas Safe engineer. This is a control wiring fault, not a boiler fault |
| F.83 | Dry fire - when the burner starts, the temperature change seen at the flow or return sensor is absent or too small (Energy7 and Easicom 3 label this Fault: Dry fire; Betacom 3 labels it Fault: Burner temperature sensor) | Check the pressure gauge reads 1.0-1.5 bar cold and top up via the filling loop if it is low. You may press reset ONCE. If it returns, stop and book a Gas Safe engineer |
| F.84 | Flow and return temperature sensor readings are not consistent with each other (difference less than -6 K) (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer |
| F.85 | Temperature sensor fault - the flow and/or return sensors appear to be on the same or the wrong pipe (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer |
| F.86 | Underfloor heating contact fault - the safety contact for the underfloor circuit is open (Energy, Energy7, Easicom 3, Betacom 3 - underfloor heating installations) | No — book a Gas Safe or underfloor heating engineer |
| F.87 | Electrode fault - the ignition electrode is not connected or is connected incorrectly (Energy, Energy7, Easicom 3 (Fault: Electrodes); Betacom 3 (Fault: Ignition electrode)) | No — book a Gas Safe engineer. Never touch the electrode or ignition lead yourself |
| F.88 | Gas valve fault - the gas valve assembly is not connected or is connected incorrectly (Energy, Energy7, Easicom 3, Betacom 3) | This is a gas valve fault. Stop using the boiler and call a Gas Safe engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999 |
| F.89 | Pump fault - the pump is not connected, is connected incorrectly, or is the wrong pump (Energy, Energy7, Easicom 3, Betacom 3) | No — book a Gas Safe engineer |
| con / Connection | No communication between the main PCB and the user interface / display (Energy, Energy7, Easicom 3, Betacom 3) | You may press reset ONCE. If the display still shows no connection, book a Gas Safe engineer |
Main fault codes
Main (Eco Compact, Eco Elite) is part of the Baxi Heating family and uses E-prefixed codes.
| Code | What it means | Safe to try yourself? |
|---|---|---|
| E09 | The boiler has detected a problem with the gas valve connection cable (Eco Compact) | No — book a Gas Safe engineer |
| E15 | The boiler is reporting a gas valve fault (Eco Compact) | No — book a Gas Safe engineer. If you can smell gas, stop using the boiler and call the National Gas Emergency Service on 0800 111 999 |
| E20 | Central heating temperature sensor (NTC) fault | No — book a Gas Safe engineer |
| E28 | Flue temperature sensor (NTC) fault (Eco Compact) | No — book a Gas Safe engineer |
| E28 | Incorrect PCB fitted (PCB fault) (Eco Elite) | No — book a Gas Safe engineer |
| E40 | Central heating return temperature sensor (NTC) fault (Eco Compact) | No — book a Gas Safe engineer |
| E50 | Hot water temperature sensor (NTC) fault (Eco Elite) | No — book a Gas Safe engineer |
| E109 | Pre-circulation fault - the boiler detected a problem circulating water before firing (Eco Compact) | Check the pressure gauge; if below 1 bar, top up to 1-1.5 bar via the filling loop. If the code stays, book a Gas Safe engineer |
| E110 | The safety thermostat has operated - the boiler has overheated and locked out | You may try ONE reset (hold the reset control for about 5 seconds). If it does not clear or it comes back, stop and book a Gas Safe engineer - do not keep resetting |
| E118 | Primary system water pressure is too low (Eco Compact) | Top up the system to 1-1.5 bar using the filling loop, then close both taps. If pressure keeps dropping, book a Gas Safe engineer |
| E119 | Water pressure switch not operated - primary water pressure is below 0.5 bar (Eco Elite) | Top up the system to 1-1.5 bar using the filling loop, then close both taps. If pressure keeps dropping, book a Gas Safe engineer |
| E125 | Circulation fault in the primary circuit | Check the pressure gauge; if below 1 bar, top up to 1-1.5 bar via the filling loop and check radiator valves are open. If the code stays, book a Gas Safe engineer |
| E128 | Flame failure - the flame was lost while the burner was running (Eco Compact) | Check other gas appliances work and, in freezing weather, thaw an EXTERNAL condensate pipe with warm (not boiling) water. You may try ONE reset; if it returns, stop and book a Gas Safe engineer. If you can smell gas, call 0800 111 999 |
| E130 | The flue temperature sensor has operated - the flue side has run too hot (Eco Compact) | No — stop using the boiler and book a Gas Safe engineer, as this involves the flue/combustion side |
| E133 | Interruption of gas supply, ignition failure or flame not detected | Check the gas is on, other gas appliances work and any prepayment meter has credit; in freezing weather thaw an EXTERNAL condensate pipe with warm (not boiling) water. Then try ONE reset (hold about 5 seconds). If it does not relight or the code returns, stop and book a Gas Safe engineer. If you can smell gas, call the National Gas Emergency Service on 0800 111 999 |
| E135 | Interruption of gas supply (internal error) (Eco Compact) | No — book a Gas Safe engineer. If you can smell gas, stop using the boiler and call 0800 111 999 |
| E160 | Fan fault or fan wiring fault | No — stop using the boiler and book a Gas Safe engineer, as the fan is part of the flue safety system |
| E321 | Hot water temperature sensor (NTC) fault (Eco Compact) | No — book a Gas Safe engineer |
| E384 | False flame - the boiler detects a flame when the burner should be off (Eco Compact) | No — stop using the boiler and book a Gas Safe engineer. If you can smell gas, call the National Gas Emergency Service on 0800 111 999 |
Potterton fault codes
Potterton (Promax, Titanium, Gold) is part of the Baxi Heating family and uses E-prefixed codes.
| Code | What it means | Safe to try yourself? |
|---|---|---|
| E20 | Central heating temperature sensor (CH NTC) fault - the boiler cannot read its heating water temperature (Promax / Titanium (verified in official user and installer guides); Gold Combi HE uses the same table) | No — book a Gas Safe engineer |
| E28 | Flue sensor fault, air pressure switch fault, blocked flue, blocked condensate drain or associated wiring fault (Promax / Titanium (verified); Gold Combi HE same table) | In freezing weather only: thaw an EXTERNAL condensate pipe with warm (not boiling) water, then try ONE reset. Otherwise stop using the boiler and call a Gas Safe engineer, as a blocked flue is possible |
| E50 | Domestic hot water temperature sensor (DHW NTC) fault (Promax / Titanium (verified); Gold Combi HE same table) | No — book an engineer (heating may still run on some models) |
| E110 | Safety (overheat) thermostat has operated - the primary heating water has overheated (Promax / Titanium (verified); Gold Combi HE same table) | Try ONE reset (hold the selector in Reset for at least 5 seconds). If it will not relight or the code returns, stop and book a Gas Safe engineer - do not keep resetting |
| E119 | Water pressure switch not operated - central heating system pressure has fallen below 0.5 bar (Promax / Titanium (verified); Gold Combi HE same table) | Top up the system via the filling loop to between 1 and 1.5 bar (boiler cold), then remove the loop. If it needs topping up repeatedly, there is a leak - book an engineer |
| E125 | Primary circulation fault - the boiler lit but water is not circulating properly (temperature failed to rise, or overshot the setpoint) (Promax / Titanium (verified, incl. detailed definition in Titanium service manual); Gold Combi HE same table) | Check the pressure gauge and top up via the filling loop if below 1 bar; if the code stays, book an engineer |
| E130 | Flue temperature sensor has operated - the flue system has overheated (Promax / Titanium (verified); Gold Combi HE same table) | Try ONE reset (hold Reset for 5 seconds). If the code returns, stop using the boiler and call a Gas Safe engineer - this involves the flue system |
| E133 | Interruption of the gas supply, ignition failure, or flame not detected (Promax / Titanium (verified); Gold Combi HE same table) | Check the gas supply is on and other gas appliances work; in freezing weather thaw an EXTERNAL condensate pipe with warm (not boiling) water; then try ONE reset (hold 5 seconds). If it will not relight, book a Gas Safe engineer. If you smell gas, stop, and call the National Gas Emergency Service on 0800 111 999 |
| E160 | Fan fault or fan wiring fault (Promax / Titanium (verified); Gold Combi HE same table) | No — book an engineer |
| E193 | Pre-circulation fault - the boiler detected a circulation problem during its pre-fire pump check (Titanium (listed in official Titanium installation and service manual)) | Check the pressure gauge and top up via the filling loop if below 1 bar; otherwise book an engineer |
| E09 | Gas valve connection fault (Baxi/Potterton shared E-code platform (official Baxi list for 'other models including Potterton')) | No — book an engineer |
| E10 | External (outdoor) temperature probe fault (Baxi/Potterton shared E-code platform) | No — book an engineer (heating may still run at default settings) |
| E15 | Gas valve command (drive) fault (Baxi/Potterton shared E-code platform) | No — book an engineer |
| E40 | Return central heating temperature sensor fault (short or open circuit) (Baxi/Potterton shared E-code platform) | No — book an engineer |
| E83-E87 | Communication fault between the boiler and its remote/room control (Baxi/Potterton shared E-code platform) | Check the room thermostat or programmer has fresh batteries and is calling for heat; if the code stays, book an engineer |
| E109 | Pre-circulation alarm - a circulation problem detected before ignition (Baxi/Potterton shared E-code platform) | Check the pressure gauge and top up via the filling loop if below 1 bar; otherwise book an engineer |
| E118 | Low water pressure in the heating circuit (below 0.5 bar) (Baxi/Potterton shared E-code platform (some models show E118 for low pressure; Promax/Titanium/Gold show E119)) | Top up the system via the filling loop to between 1 and 1.5 bar (boiler cold). If it keeps dropping, there is a leak - book an engineer |
| E128 | Safety lockout for repeated loss of flame during operation (Baxi/Potterton shared E-code platform) | Stop using the boiler and call a Gas Safe engineer - this is a combustion-related lockout. Do not repeatedly reset it |
| E129 | Safety lockout for frequent flame loss during ignition (with maximum correction applied) (Baxi/Potterton shared E-code platform) | Stop using the boiler and call a Gas Safe engineer - do not repeatedly reset |
| E134 | Gas valve was open but no gas was detected within the allowed time (Baxi/Potterton shared E-code platform) | Check the gas supply is on and other gas appliances work; try ONE reset. If it recurs, book a Gas Safe engineer. If you smell gas call 0800 111 999 |
| E135 | Internal (PCB/electronics) error (Baxi/Potterton shared E-code platform) | No — book an engineer |
| E154 | Flow/return plausibility check failed - temperatures do not make sense against each other (Baxi/Potterton shared E-code platform) | Check the pressure gauge and top up via the filling loop if below 1 bar; otherwise book an engineer |
| E270 | Dry fire detected - the boiler fired with little or no water passing through it (Baxi/Potterton shared E-code platform) | Check the pressure gauge and top up via the filling loop if low; if the code returns, stop and book an engineer |
| E317 (162) | Incorrect electrical supply frequency detected (Baxi/Potterton shared E-code platform) | No — book an engineer |
| E321 (163) | Domestic hot water temperature sensor fault (short or open circuit) (Baxi/Potterton shared E-code platform) | No — book an engineer |
| E384 (164) | False flame detected - the boiler senses a flame when there should not be one (Baxi/Potterton shared E-code platform) | Stop using the boiler and call a Gas Safe engineer - this is a combustion/gas-control concern. If you smell gas call the National Gas Emergency Service on 0800 111 999 |
| E385 (165) | Supply under-voltage detected (Baxi/Potterton shared E-code platform) | No — beyond checking other electrics in the house work normally - if it persists, book an engineer |
| E430 (166) | Water pressure test failed or temporary water pressure fault (Baxi/Potterton shared E-code platform) | Check the pressure gauge and top up via the filling loop to 1-1.5 bar; if the code returns, book an engineer |
Viessmann fault codes
Viessmann (Vitodens) has used two different code schemes across generations — the same number can mean different things on different models, so always check against the model on the data plate. Codes below note which range they apply to.
| Code | What it means | Safe to try yourself? |
|---|---|---|
| 0A | The CO limiter (where fitted) has responded because the carbon monoxide concentration is too high - or, on models with a gas pressure switch, the gas pressure is too low. Either way the burner is blocked (Vitodens 100-W (B1HC/B1KC) - only where a CO limiter is fitted) | Stop using the boiler, turn it off, open windows and call a Gas Safe registered engineer immediately - if you smell gas or feel unwell, leave the property and call the National Gas Emergency Service on 0800 111 999. Do not reset it |
| 0b | The burner is blocked because of inadequate water flow through the boiler (Vitodens 100-W (B1HA/B1KA)) | Check the pressure gauge and top up via the filling loop if it is below the normal band, then try one reset - if it returns, book a Gas Safe registered engineer |
| 0C | The burner is blocked because the mains supply voltage is too low (Vitodens 111-W (B1LB) and Vitodens 100-W (B1HC/B1KC)) | Check the boiler's fused spur or switch is on and that no breaker has tripped at the consumer unit, then try one reset - if it returns, book a Gas Safe registered engineer |
| 10 | Short circuit on the outside temperature sensor; the boiler runs in constant/continuous mode (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | No — book an engineer. The boiler will usually keep heating, but weather compensation is lost |
| 18 | Lead break (open circuit) on the outside temperature sensor; the boiler runs in constant/continuous mode (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | No — book an engineer |
| 30 | Short circuit on the boiler water temperature sensor; the burner is blocked (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | No — book an engineer |
| 38 | Lead break (open circuit) on the boiler water temperature sensor; the burner is blocked (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | No — book an engineer |
| 50 | Short circuit on the cylinder (DHW storage) temperature sensor; no hot water heating (Vitodens 100-W (B1HC/B1KC) and 111-W (B1LB) - cylinder/storage models) | No — book an engineer. Central heating will normally still work |
| 51 | Short circuit on the outlet (domestic hot water outlet) temperature sensor; no hot water heating (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | No — book an engineer |
| 52 | Short circuit on the flow sensor (domestic hot water flow turbine); the burner is blocked (Vitodens 050-W (BPJD) and 100-W (B1HC/B1KC) combi models) | No — book an engineer |
| 58 | Lead break (open circuit) on the cylinder temperature sensor; no hot water heating (Vitodens 100-W (B1HC/B1KC) and 111-W (B1LB) - cylinder/storage models) | No — book an engineer |
| 59 | Lead break (open circuit) on the outlet temperature sensor; no hot water heating (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB) - see note on the newer B0KA range) | No — book an engineer |
| 5A | Lead break (open circuit) on the flow sensor; the burner is blocked (Vitodens 050-W (BPJD) and 100-W (B1HC/B1KC) combi models) | No — book an engineer |
| A3 | The flue gas temperature sensor is incorrectly positioned and the burner is blocked (Vitodens 100-W (B1HC/B1KC)) | Stop using the boiler and call a Gas Safe registered engineer - this is a flue-related fault and there is nothing safe for you to check |
| A9 | Communication error with the OpenTherm device; the boiler runs in control mode without OpenTherm influence (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | Check your room thermostat or programmer has good batteries and is calling for heat, then try one reset - if it returns, book an engineer |
| b0 | Short circuit on the flue gas temperature sensor; the burner is blocked (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | Stop using the boiler and call a Gas Safe registered engineer - this is a flue-related fault and there is nothing safe for you to check |
| b7 | Burner control unit fault; the appliance drops into emergency mode (Vitodens 100-W (B1HC/B1KC)) | Try switching the boiler off at its switch and back on once - if the fault returns, book a Gas Safe registered engineer. Do not repeat this |
| b8 | Lead break (open circuit) on the flue gas temperature sensor; the burner is blocked (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | Stop using the boiler and call a Gas Safe registered engineer - this is a flue-related fault and there is nothing safe for you to check |
| E3 | A fault in the safety chain has put the burner into a fault state (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | No — book a Gas Safe registered engineer. Do not keep pressing reset on a lockout |
| E5 | Internal fault in the control; the burner is blocked (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | One reset attempt only - if the fault returns, book a Gas Safe registered engineer |
| F0 | Internal fault in the control unit; the burner is blocked (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | One reset attempt only - if the fault returns, book a Gas Safe registered engineer |
| F1 | Maximum flue gas temperature has been exceeded and the burner has gone to a fault state (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | Stop using the boiler and call a Gas Safe registered engineer - this is a flue gas temperature fault and must not be repeatedly reset |
| F2 | The temperature limiter (overheat/high limit) has responded and the burner is in a fault state (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | Check the pressure gauge and top up via the filling loop if it is below the normal band, then try one reset - if it locks out again, do not keep resetting; book a Gas Safe registered engineer |
| F3 | A flame signal was already present at burner start, so the burner has locked out (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | Stop using the boiler and call a Gas Safe registered engineer - if you smell gas, leave the property and call 0800 111 999. Do not keep resetting |
| F4 | No flame signal is present, so the burner has locked out on ignition failure (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | Check the gas supply is on, that other gas appliances work and any prepayment meter has credit, then try ONE reset - if it locks out again do not keep resetting; book a Gas Safe registered engineer. If you smell gas, call 0800 111 999 |
| F8 | The fuel (gas) valve closes too late and the burner is in a fault state (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | Stop using the boiler and call a Gas Safe registered engineer - this is a gas valve safety fault. If you smell gas, leave the property and call 0800 111 999 |
| F9 | Fan speed was too low during burner start and the burner is in a fault state (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | One reset attempt only - if the fault returns, book a Gas Safe registered engineer |
| FA | The fan has not reached idle state (has not come to a standstill) and the burner is in a fault state (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | One reset attempt only - if the fault returns, book a Gas Safe registered engineer |
| FC | Electrical fan control (control unit) is faulty and the burner is blocked (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | One reset attempt only - if the fault returns, book a Gas Safe registered engineer |
| Fd | Burner control unit fault; the burner is blocked (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | One reset attempt only - if the fault returns, book a Gas Safe registered engineer |
| FF | Burner control unit fault; the burner is blocked (Vitodens 050-W (BPJD), 100-W (B1HC/B1KC), 111-W (B1LB)) | One reset attempt only - if the fault returns, book a Gas Safe registered engineer |
| --- | Communication error between the burner control unit and the programming unit; the burner is blocked (Vitodens 050-W (BPJD) - dashes shown in the display) | One reset attempt only - if the display still shows dashes, book a Gas Safe registered engineer |
| F.62 | The high limit safety cut-out has responded and the burner is in a fault state (Vitodens 050-W (B0KA/BPKA/B0KA-M) - newer numeric code range) | Check the pressure gauge and top up via the filling loop if it is below the normal band, then try one reset - if it locks out again, book a Gas Safe registered engineer |
| F.63 | The flue gas temperature limiter has responded and the burner is in a fault state (Vitodens 050-W (B0KA/BPKA/B0KA-M) - newer numeric code range) | Stop using the boiler and call a Gas Safe registered engineer - this is a flue gas temperature fault and must not be repeatedly reset |
| F.67 | Ionisation current lies outside the permissible range and the burner is in a fault state (Vitodens 050-W (B0KA/BPKA/B0KA-M) - newer numeric code range) | Stop using the boiler and call a Gas Safe registered engineer - this is a combustion fault. If you smell gas, leave the property and call 0800 111 999 |
| F.68 | A flame signal is already present at burner start and the burner is in a fault state (Vitodens 050-W (B0KA/BPKA/B0KA-M) - newer numeric code range) | Stop using the boiler and call a Gas Safe registered engineer - if you smell gas, leave the property and call 0800 111 999. Do not keep resetting |
| F.71 | Fan speed is too low and the burner is in a fault state (Vitodens 050-W (B0KA/BPKA/B0KA-M) - newer numeric code range) | One reset attempt only - if the fault returns, book a Gas Safe registered engineer |
| F.74 | System pressure is too low; the burner is locked out and the internal circulation pump is off, so there is no heating and no hot water (Vitodens 050-W (B0KA/BPKA/B0KA-M) - newer numeric code range) | Top up the system pressure using the filling loop until the gauge is in the normal band and bleed radiators if needed - if the pressure keeps dropping, book an engineer to find the leak |
| F.345 | The temperature limiter has responded; the burner is locked out with automatic re-enabling once the appliance has cooled down (Vitodens 050-W (B0KA/BPKA/B0KA-M) - newer numeric code range) | Check the pressure gauge and top up via the filling loop if it is below the normal band, then let the boiler cool and try one reset - if it locks out again, book a Gas Safe registered engineer |
Ferroli fault codes
Ferroli (Modena, Optimax, Bluehelix) uses A-prefixed lockout codes and F-prefixed fault codes.
| Code | What it means | Safe to try yourself? |
|---|---|---|
| A01 | Burner lockout - the boiler tried to light and no flame was detected, so it has shut down and locked out | Check the gas is on at the meter and that other gas appliances work, and if the condensate pipe runs outside and is frozen, thaw it with warm (not boiling) water. Then ONE reset attempt only. If it locks out again, stop and book a Gas Safe engineer - do not keep resetting. If you smell gas at any point, do not touch any switches: leave the property and call the National Gas Emergency Service on 0800 111 999 |
| A02 | The control board is seeing a flame signal when the burner should be off - a safety lockout | No — book a Gas Safe engineer. Do not reset repeatedly. If you smell gas, leave the property and call the National Gas Emergency Service on 0800 111 999 |
| A03 | High limit (overheat) protection has operated and shut the boiler down (Modena S/C HE and Optimax HE Plus only) | Check the system pressure gauge and top up via the filling loop if it is below the mark on the gauge, and check the room thermostat is calling for heat and has good batteries. Nothing further is safe - book a Gas Safe engineer |
| A04 | Flue gas fault lockout, triggered because the F07 high flue temperature fault has occurred three times in the last 24 hours (Modena S/C HE and Optimax HE Plus only) | Stop using the boiler and book a Gas Safe engineer - this is a flue and combustion concern. Do not keep resetting it |
| A05 | Fan fault - the boiler has lost or lost confidence in the fan speed signal and shut down | No — book a Gas Safe engineer. The fan is a flue safety component, so do not attempt to reset repeatedly |
| A06 | The burner lit but the flame was then lost, and the boiler has locked out | If the condensate pipe runs outside and is frozen, thaw it with warm (not boiling) water, then ONE reset attempt only. Otherwise nothing safe to try - book a Gas Safe engineer, and never reset repeatedly. If you smell gas, leave the property and call the National Gas Emergency Service on 0800 111 999 |
| F07 / A07 | High flue gas temperature - the flue probe has measured an excessive temperature | Stop using the boiler and book a Gas Safe engineer - this is a flue and combustion concern |
| F08 / A08 | Over-temperature protection has operated on the heating (flow) sensor circuit (Bluehelix Tech RRT) | Check the pressure gauge and top up via the filling loop if it is low. Nothing further is safe - book a Gas Safe engineer |
| F09 / A09 | Over-temperature protection has operated on the return sensor circuit (Bluehelix Tech RRT) | Check the pressure gauge and top up via the filling loop if it is low. Nothing further is safe - book a Gas Safe engineer |
| F10 / A10 | Flow (heating) temperature sensor fault - the sensor reading is out of range | No — book a Gas Safe engineer |
| F11 / A11 | Return temperature sensor fault - the sensor reading is out of range | No — book a Gas Safe engineer |
| F12 | Domestic hot water sensor fault - the DHW sensor reading is out of range (Combi models - Modena C HE, Optimax HE Plus C, Bluehelix Tech RRT C) | No — book a Gas Safe engineer. Heating may still work but hot water performance will be affected |
| F13 / A13 | Flue gas probe fault - the flue/exchanger probe reading is out of range | No — book a Gas Safe engineer. This probe is a flue safety device, so do not keep resetting |
| F14 | On Modena and Optimax this is a flow sensor fault; on Bluehelix Tech RRT it is listed together with F07/A07 as high flue gas temperature (Meaning differs by series - see notes) | No — book a Gas Safe engineer. On a Bluehelix boiler treat this as a flue concern and stop using the appliance |
| A14 | Flue extraction duct safety device has operated, triggered by fault F07 occurring three times in the last 24 hours (Bluehelix Tech RRT) | Stop using the boiler and book a Gas Safe engineer - this is a flue and combustion concern. Do not keep resetting |
| F15 | On Modena and Optimax this is a fan problem; on Bluehelix Tech RRT it is grouped with F20 and F21 as a PCB parameter fault (Meaning differs by series - see notes) | No — book a Gas Safe engineer |
| F34 | Mains supply voltage has fallen below 170V | Check the boiler's fused spur switch is on and that the rest of the house has power - if other circuits are affected this is an electrical supply issue. Do not open the boiler; if it persists, book a Gas Safe engineer |
| F35 | Irregular mains frequency detected on the electrical supply (Modena S/C HE and Optimax HE Plus only) | Check the boiler's fused spur switch is on and that the house electrics are working normally. Nothing further is safe - book a Gas Safe engineer if it persists |
| F37 | System water pressure is incorrect - it has dropped below the minimum needed for the boiler to run | This one is usually a homeowner fix. Check the pressure gauge and, using the filling loop, top the system up to the pressure marked on the gauge or in your user guide (typically around 1.0-1.5 bar cold), then close the filling loop. One reset if needed. If the pressure keeps dropping, you have a leak - book a Gas Safe engineer |
| F39 | Fault with the optional external (outdoor) temperature probe (Modena C HE, Optimax HE Plus, Bluehelix Tech RRT (optional outdoor sensor)) | No — book a Gas Safe engineer. The boiler will usually still heat, just without weather compensation |
| A41 | Flow sensor disconnected - the boiler cannot see the flow temperature sensor (Modena S/C HE and Optimax HE Plus only) | No — book a Gas Safe engineer |
| F41 | Maximum delta T protection has activated - too large a temperature difference between flow and return (Bluehelix Tech RRT) | Check the pressure gauge and top up via the filling loop if it is low, and make sure radiator valves have not been left closed. Nothing further is safe - book a Gas Safe engineer |
| F42 / A42 | On Modena and Optimax this is a flow sensor fault (sensor damaged); on Bluehelix Tech RRT it is sensor control protection activation (Meaning differs by series - see notes) | No — book a Gas Safe engineer |
| F43 | Heat exchanger protection has activated to stop the exchanger being damaged | Check the pressure gauge and top up via the filling loop if it is low, and check radiator valves are open. Nothing further is safe - book a Gas Safe engineer |
| F50 (with A23, A24, A26, F15, F20, F21, F40, F47) | PCB parameter fault - the control board is running with an incorrect parameter setting (Bluehelix Tech RRT) | No — book a Gas Safe engineer |
| F51 - F53 | Calibration fault - the boiler's automatic combustion calibration has not completed correctly (Bluehelix Tech RRT) | No — book a Gas Safe engineer. This is a combustion setting fault, so do not attempt to reset it repeatedly |
| F56 / A56 | The calibration procedure did not complete (Bluehelix Tech RRT) | No — book a Gas Safe engineer. This is a combustion setting fault |
| F61 / A61 | Internal control board fault | No — book a Gas Safe engineer |
| A62 | No communication between the control board and the gas valve | Stop using the boiler and book a Gas Safe engineer - this involves the gas valve. If you smell gas, leave the property and call the National Gas Emergency Service on 0800 111 999 |
| A63 | Internal control board fault | No — book a Gas Safe engineer |
| A64 | On Bluehelix Tech RRT this means the maximum number of consecutive resets has been exceeded; on Modena and Optimax it is listed as an ABM03 controller fault (Meaning differs by series - see notes) | Stop resetting - repeated resets on a lockout are dangerous. Book a Gas Safe engineer to find the underlying fault |
| F66 | On Bluehelix Tech RRT: firmware was not loaded successfully onto the control board. On Modena and Optimax: ABM03 controller internal fault | No — book a Gas Safe engineer |
| F67 | Parameter loading fault associated with the BCC Service key being connected (Bluehelix Tech RRT) | No — book a Gas Safe engineer |
| F68 / A68 | BCC Service key error - the boiler could not read the file from the service key (Bluehelix Tech RRT) | No — book a Gas Safe engineer |
Vokera fault codes
Vokèra (Easi-Heat, Vision, Compact) uses A-prefixed codes on current models.
| Code | What it means | Safe to try yourself? |
|---|---|---|
| A10 / E010 | Flame lockout - the boiler tried to light, did not detect a flame, and has shut down and locked out; the same code also covers a blocked condensate drain and a blocked flue outlet or air inlet (Easi-Heat i 25C/29C/20S/25S (A10); Vision Plus 20S/25S/30S/25C/30C/35C/40C (E010)) | Check the gas is on and other gas appliances (hob, fire) still work, and if the condensate pipe running outside the house is frozen, pour warm - not boiling - water along it. Then try ONE reset. If it locks out again, stop using the boiler and book a Gas Safe registered engineer - do not keep resetting. If you can smell gas, leave the gas off, open windows and call the National Gas Emergency Service on 0800 111 999 |
| A11 / E011 | Extraneous (false) flame - the PCB is detecting a flame signal when the burner should be off (Easi-Heat i (A11); Vision Plus (E011); Vision S and Compact A show A11 as "False flame") | No — book a Gas Safe registered engineer |
| A20 / E020 | Limit (overheat) thermostat has operated and the boiler has locked out (Easi-Heat i (A20); Vision Plus (E020)) | Check the pressure gauge reads about 1 to 1.5 bar when the boiler is cold and top up via the filling loop if it is low. Then try ONE reset. If the code returns, book a Gas Safe registered engineer - do not keep resetting |
| A30 / E030 | Fan fault - the fan is not running at the speed the PCB has commanded, or no tacho signal is being received (Easi-Heat i (A30); Vision Plus (E030)) | You may make ONE reset attempt. If the code returns, stop using the boiler and book a Gas Safe registered engineer - the fan is a combustion safety component and repeated resetting is dangerous |
| A40 / E040 | System water pressure has fallen too low and the boiler has stopped - the display asks you to fill the system (Easi-Heat i (A40); Vision Plus (E040)) | Top the system up using the filling loop until the gauge reads 1 to 1.5 bar with the boiler cold, then close and disconnect the filling loop and reset once. If the pressure keeps dropping there is a leak - book an engineer rather than topping up repeatedly |
| A41 / E041 | Temporary low water pressure warning - pressure has dropped below about 0.3 bar; if it is not corrected within roughly 10 minutes the boiler changes to the permanent A40 / E040 fault (Easi-Heat i (A41); Vision Plus (E041)) | Top the system up using the filling loop to 1 to 1.5 bar with the boiler cold, then close and disconnect the filling loop. If you have to do this often, there is a leak - book an engineer |
| A42 / E042 | Pressure transducer (water pressure sensor) fault - the boiler cannot read system pressure reliably (Easi-Heat i (A42); Vision Plus (E042)) | No — book an engineer |
| A58 / A59 | Mains supply voltage to the boiler is too low (A58) or too high (A59) (Easi-Heat i) | No — book an engineer. Do not open the boiler or touch any wiring |
| A60 / E060 | Domestic hot water probe fault - the hot water sensor has failed; the boiler will normally keep supplying hot water at around 50C (Easi-Heat i (A60); Vision Plus (E060)) | No — book an engineer. The boiler will usually still give hot water at a fixed temperature in the meantime |
| A70 / E070 | Flow (primary) sensor group fault - covers flow sensor failure, flow sensor over-temperature, and an abnormal flow/return temperature differential (Easi-Heat i (A70); Vision Plus (E070)) | Check the pressure gauge reads about 1 to 1.5 bar cold and top up via the filling loop if low, then try ONE reset. If the code returns, book an engineer |
| A77 / E077 | The external low-temperature / zone water safety thermostat has operated or its circuit has failed (Vision S and Compact A show A77 (low temperature thermostat fault); Vision Plus shows E077 (water thermostat, main zone or zone 1)) | No — book an engineer |
| A80 / E080 | Return sensor group fault - covers return probe failure, return probe over-temperature, and an inverted or abnormal return/flow differential (Easi-Heat i (A80); Vision Plus (E080)) | Check the pressure gauge reads about 1 to 1.5 bar cold and top up via the filling loop if low, then try ONE reset. If the code returns, book an engineer |
| A90 / E090 | Flue gas probe fault or flue gas over-temperature (Easi-Heat i (A90); Vision Plus (E090)) | Stop using the boiler and book a Gas Safe registered engineer - this involves the flue and combustion. If you can smell gas or fumes, ventilate, turn the gas off and call the National Gas Emergency Service on 0800 111 999 |
| A91 / E091 | Service warning that the primary heat exchanger needs cleaning - triggered when the internal counter passes 2500 hours in defined operating conditions (Easi-Heat i (A91); Vision Plus (E091)) | No — this is a maintenance warning. Book a Gas Safe registered engineer to service the boiler |
| CFS / _CL | Service reminder - the boiler is signalling that its scheduled service interval has been reached (Easi-Heat i (CFS); Vision S and Compact A (_CL, "Call for service")) | No — book your annual boiler service with a Gas Safe registered engineer |
| SFS / _St | The boiler has stopped and will not run until it has been serviced - a definitive service lockout (Easi-Heat i (SFS, "Stop for service"); Vision S and Compact A (_St, "Autostop")) | No — book a Gas Safe registered engineer. Do not attempt to reset it repeatedly |
| FIL | Low system pressure signal - the display is prompting you to top the heating system up (Easi-Heat i (FIL); Vision Plus (<0,6 bar)) | Top up using the filling loop to 1 to 1.5 bar with the boiler cold, then close and disconnect the filling loop. If you need to do this more than very occasionally, book an engineer to find the leak |
| >3.0 bar | High system pressure signal - system pressure has risen above about 3 bar (Easi-Heat i; Vision Plus (>3,0 bar)) | Check the filling loop is fully closed and disconnected. If the pressure stays above 3 bar, book an engineer - do not attempt to drain or bleed the system yourself |
| AL10 | Ignition failure - no flame sensed, or the condensate sensor has operated; the boiler has locked out (Easi-Heat Plus (18V and C/Ci range)) | Check the gas is on and other gas appliances still work, and if the condensate pipe outside the house is frozen, pour warm - not boiling - water along it. Then try ONE reset. If it locks out again, stop using the boiler and book a Gas Safe registered engineer. If you can smell gas, turn the gas off, ventilate and call 0800 111 999 |
| AL20 | Limit thermostat or flue thermostat fault - an overheat safety device has operated and the boiler has locked out (Easi-Heat Plus) | Check the pressure gauge reads about 1 to 1.5 bar cold and top up via the filling loop if low, then try ONE reset. If the code returns, stop using the boiler and book a Gas Safe registered engineer - the flue thermostat is a combustion safety device |
| AL21 | External device fault (UHT / CPA) - an external safety device such as an underfloor high-limit thermostat or condensate pump alarm has operated (Easi-Heat Plus) | No — book an engineer |
| AL26 | Return temperature too high (Easi-Heat Plus) | Check the pressure gauge reads about 1 to 1.5 bar cold and top up via the filling loop if low, then try ONE reset. If the code returns, book an engineer |
| AL28 | Temperature differential inverted - the return sensor is reading hotter than the flow sensor (Easi-Heat Plus) | Check the pressure gauge reads about 1 to 1.5 bar cold and top up via the filling loop if low, then try ONE reset. If the code returns, book an engineer |
| AL34 | Fan tacho signal fault (Easi-Heat Plus) | You may make ONE reset attempt. If the code returns, stop using the boiler and book a Gas Safe registered engineer - do not keep resetting a fan or flue fault |
| AL52 | Internal fault within the boiler control (Easi-Heat Plus) | No — book an engineer. The user manual for this appliance says to call an engineer rather than reset |
| AL55 | Jumper tag (configuration link) fault - final alarm (Easi-Heat Plus) | No — book an engineer |
| AL60 | On system boilers (e.g. Mynute VHE): jumper tag (configuration link) fault - temporary alarm. On Unica combi models: domestic hot water thermistor fault (Easi-Heat Plus) | No — book an engineer |
| AL71 | Primary (flow) thermistor fault (Easi-Heat Plus) | No — book an engineer |
| AL73 | Return thermistor fault (Easi-Heat Plus) | No — book an engineer |
| AL74 | No water circulation detected (system models such as Mynute VHE) or over-temperature due to low water pressure (Unica combi models) (Easi-Heat Plus) | Check the pressure gauge reads about 1 to 1.5 bar cold and top up via the filling loop if low, then try ONE reset. If the code returns, book an engineer |
| AL79 | Flow temperature too high, or the differential between flow and return is too great (Easi-Heat Plus) | Check the pressure gauge reads about 1 to 1.5 bar cold and top up via the filling loop if low, then try ONE reset. If the code returns, book an engineer |
| A01 | Ignition failure - flame not sensed, or internal fault; the boiler has locked out (Vision S 20/25, Compact A 25/29 and related A-code models) | Check the gas is on and other gas appliances still work, and if the condensate pipe outside is frozen, pour warm - not boiling - water along it. Then try ONE reset. If it locks out again, stop using the boiler and book a Gas Safe registered engineer. If you can smell gas, turn the gas off, ventilate and call 0800 111 999 |
| A02 | Limit thermostat fault - the overheat thermostat has operated and the boiler has locked out (Vision S, Compact A) | Check the pressure gauge reads about 1 to 1.5 bar cold and top up via the filling loop if low, then try ONE reset. If the code returns, book a Gas Safe registered engineer - do not keep resetting |
| A03 | Fan tacho signal fault - the PCB is not receiving correct speed feedback from the fan (Vision S, Compact A) | You may make ONE reset attempt. If the code returns, stop using the boiler and book a Gas Safe registered engineer |
| A04 | Insufficient system water pressure (Vision S, Compact A) | Top up using the filling loop to 1 to 1.5 bar with the boiler cold, close and disconnect the filling loop, then reset once. If pressure keeps dropping there is a leak - book an engineer instead of topping up repeatedly |
| A06 | On Compact A combis this is a domestic hot water thermistor fault; on Vision S system boilers the same code reports an incorrect jumper tag configuration (Compact A: DHW thermistor fault. Vision S: jumper tag configuration) | No — book an engineer |
| A07 | Primary (flow) thermistor group fault - covers flow thermistor failure, flow thermistor over-temperature, and an abnormal temperature differential (Vision S, Compact A) | Check the pressure gauge reads about 1 to 1.5 bar cold and top up via the filling loop if low, then try ONE reset. If the code returns, book an engineer |
| A08 | Return thermistor group fault - covers return thermistor failure, return thermistor over-temperature, and an inverted temperature differential (Vision S, Compact A) | Check the pressure gauge reads about 1 to 1.5 bar cold and top up via the filling loop if low, then try ONE reset. If the code returns, book an engineer |
| A09 | Flue thermistor or flue thermistor counter fault, or flue thermistor over-temperature (Vision S, Compact A) | Stop using the boiler and book a Gas Safe registered engineer - this involves the flue and combustion. If you can smell fumes or gas, ventilate, turn the gas off and call 0800 111 999 |
Biasi fault codes
Biasi (Riva, Advance) uses E-prefixed codes.
| Code | What it means | Safe to try yourself? |
|---|---|---|
| Er 01 (remote code 01E) | The boiler tried to light, failed to prove a flame, and has gone to ignition safety lockout (Advance Plus / Advance Plus ERP (LCD models 25C/30C/35C ERP). Not shown on Riva Advance HE M110/M110B, which has no display.) | Check the gas is on at the meter and other gas appliances work; if the condensate pipe outside is frozen, thaw it with warm (not boiling) water. Then press reset ONCE only. If it locks out again, stop using the boiler and book a Gas Safe engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999 |
| Er 02 (remote code 02E) | The safety (overheat) thermostat has tripped and locked the boiler out (Advance Plus / Advance Plus ERP) | Check the pressure gauge; if it has dropped below the green band, top up via the filling loop as described in your manual. Then press reset ONCE. If it trips again, stop and book a Gas Safe engineer - do not keep resetting |
| Er 03 (remote code 03E) | General safety lockout - the control has stopped the boiler for a fault it cannot categorise more precisely (Advance Plus / Advance Plus ERP) | If the external condensate pipe is frozen, thaw it with warm (not boiling) water. Press reset ONCE. If the lockout returns, stop using the boiler and book a Gas Safe engineer |
| Er 04 (remote code 04E) | Faulty primary circuit - no water or absence of flow through the boiler (Advance Plus / Advance Plus ERP) | Check the pressure gauge and top up through the filling loop if it has dropped below the green band. Press reset ONCE. If it returns, book a Gas Safe engineer |
| Er 05 (remote code 05E) | Faulty fan control system - the fan is not running at the speed the control expects (Advance Plus / Advance Plus ERP) | No — book a Gas Safe engineer. The fan controls safe combustion and flue clearance, so do not keep resetting the boiler |
| Er 06 (remote code 06E) | Faulty central heating (flow) temperature probe NTC (Advance Plus / Advance Plus ERP) | No — book a Gas Safe engineer |
| Er 07 (remote code 07E) | Faulty domestic hot water temperature probe NTC (Advance Plus / Advance Plus ERP) | No — book a Gas Safe engineer |
| Er 08 (remote code 08E) | Faulty external (outdoor) temperature probe NTC (Advance Plus / Advance Plus ERP - only where an outdoor sensor is fitted) | No — book a Gas Safe engineer. Heating usually still works, but weather compensation will not |
| Er 09 (remote code 09E) | Faulty flue temperature probe NTC (Advance Plus / Advance Plus ERP) | No — book a Gas Safe engineer. This sensor is part of the flue safety system, so do not run the boiler on repeated resets |
| Er 10 (remote code 10E) | Flue probe intervention lockout - flue gas temperature has exceeded the safe limit and the boiler has shut down (Advance Plus / Advance Plus ERP. On some Advance Plus models the trip point is stated as flue temperature above 120 C; the ERP manual quotes 110 C for the flue probe and 167 C for the flue thermal fuse.) | Stop using the boiler and book a Gas Safe engineer. This is a flue and combustion safety shutdown - do not reset it repeatedly. If you smell gas or fumes, call the National Gas Emergency Service on 0800 111 999 |
| Er 11 / An 11 (remote code 11E) | Flame detection error - the control is seeing a flame signal that does not match the burner state (Advance Plus / Advance Plus ERP. The ERP manual shows flame detection error on the LCD as An flashing with the error number; the remote control shows 11E.) | Stop using the boiler and book a Gas Safe engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999 |
| Er 12 | Faulty central heating return temperature probe NTC (Advance Plus / Advance Plus ERP (where a return sensor is fitted)) | No — book a Gas Safe engineer |
| Er 13 | Temperature difference between flow and return is greater than 40 K (Advance Plus / Advance Plus ERP) | Check the pressure gauge and top up via the filling loop if it is below the green band. If the fault stays, book a Gas Safe engineer |
| Er 14 (remote code 14E) | No circulation, faulty pump, or the primary temperature limit has been exceeded (above 105 C,) (Advance Plus / Advance Plus ERP. The official ERP manual prints Er 14 twice - once for pump failure or primary temperature above 105 C, and once for absence of flow detected from a temperature gradient greater than 2 K/s.) | Check the pressure gauge and top up through the filling loop if it has dropped. Press reset ONCE. If it returns, book a Gas Safe engineer - the boiler may need up to ten minutes before it will restart |
| Er 19 | Domestic hot water inlet probe failure (Advance Plus / Advance Plus ERP - only where a d.h.w. inlet probe is fitted) | No — book a Gas Safe engineer |
| Er 25 | Flame detection error (Advance Plus / Advance Plus ERP) | Stop using the boiler and book a Gas Safe engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999 |
| Er 69 | Wiring error lockout - the control has detected an electrical connection fault (Advance Plus / Advance Plus ERP) | No — book a Gas Safe engineer |
| Li 01 | Primary circuit temperature limit reached during hot water operation - the hot water exchanger cannot absorb the heat the boiler is producing (Advance Plus / Advance Plus ERP) | No — book a Gas Safe engineer. Heating will usually still work but hot water performance will be poor |
| FL (flashing) | Filling request - the boiler still runs but system pressure has fallen and needs topping up; if it falls further the boiler stops and shows a lack of water error (Advance Plus / Advance Plus ERP) | Top up the system through the filling loop until the pressure gauge is back within the green band, then close both filling loop valves. If you have to top up often, book a Gas Safe engineer to look for a leak |
When a code means stop, don't reset
- Any smell of gas — turn off at the meter, ventilate, leave, call 0800 111 999
- A code that returns straight after a reset
- Scorching, soot, or a carbon monoxide alarm sounding
- Water visibly leaking from the boiler itself
None of these are DIY territory, whatever the code says. Turn the boiler off and call us.
Written by Saeed Iqbal, the engineer who leads Synergy Gas & Plumbing (Gas Safe registered 594385). Last reviewed August 2026.
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Answers
Common questions
Can I fix a boiler fault code myself?
Only two things are genuinely safe to try: repressurising via the filling loop if the code points to low pressure, and thawing an accessible external condensate pipe with warm water if it's frozen. Everything else — ignition, gas valve, flue, fan, sensors, PCB — needs a Gas Safe registered engineer.
Is it safe to keep resetting my boiler?
One reset after checking pressure and the condensate pipe is reasonable. If the same code comes straight back, stop. Repeated resets on a genuine fault can wear ignition components out faster and, with some faults, aren't safe to keep repeating.
Why do fault codes differ between manufacturers?
Each manufacturer designs its own control board and diagnostic logic, so there's no universal standard — F22 means something different on a Vaillant than a Glow-worm, for instance, even though the two brands are related. Always check against your specific model.
My fault code isn't listed here — what do I do?
This guide covers the fault codes we're asked about most, not every code that exists. Check the sticker inside your boiler's casing flap or your user manual for the full list for your exact model, or call us with the code and we can usually tell you what it means over the phone.
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