Boiler Fault Codes Explained: Vaillant, Worcester, Baxi, Ideal & Glow-worm
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 condensat…
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.
Before you look up the code
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 |
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 |
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 |
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) |
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 |
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.
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Leave a number and a postcode. We will call you back — usually within the hour during office hours.
Written by the engineering team at 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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