An immersion heater is the electric element inside a hot water cylinder. When it fails you get no hot water, a cylinder that runs cold after one shower, or a breaker that trips. We test the element, its thermostat and the supply to it, and replace what has failed. In office hours (Monday to Friday, 8am to 5.30pm) the diagnosis visit is £99. Replacing an element or thermostat is not included in that: it is quoted before we start, because the price depends on the cylinder and the part. If the cylinder is unvented, such as a Megaflo, the work needs a G3 qualified engineer, and our lead engineer holds that qualification.
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Unvented cylinder repairs £99 for the first hour in office hours, parts quoted first. Immersion heater and vented cylinder repairs are quoted after a £99 diagnosis. Unvented cylinder annual service £120 (£90 with a boiler service).
No travel charge within 10 miles of B20 2JS. Further out, £2 per mile may apply — always agreed before anything is booked. Full price list
Smell gas now? Do not use this form or wait for a reply. Call the National Gas Emergency Service free on 0800 111 999 (24 hours). If you are using a mobile, make the call from outside. Open doors and windows, do not switch electrics on or off, do not smoke or use naked flames, and turn the gas off at the meter if it is safe to do so, unless the meter is in a cellar or basement. Once the supply has been made safe, we can trace and repair the fault.
It is a heating element, much like the one in a kettle, screwed into the cylinder through a threaded boss. A thermostat in the head of the element switches it off when the water reaches temperature, and a separate overheat cut-out switches it off if the thermostat fails.
Many cylinders have two. A lower element heats the whole cylinder, often overnight on a cheaper tariff, and an upper one heats the top part quickly as a daytime boost. Other cylinders are heated mainly by the boiler and have an immersion heater only as a back-up.
A cause can only be confirmed by testing, so read these as a guide to what an engineer will check.
If the immersion heater is your only source of hot water, the element, its thermostat or the overheat cut-out may have failed, or the supply may be off: the wall switch, the fuse or the timer.
With two elements, this usually means the lower one has failed and only the upper boost element is working.
An element whose insulation has broken down leaks current to earth and trips the breaker, sometimes only once it is hot. Leave it switched off at the wall. Resetting it again and again is not safe.
The thermostat has probably stuck on. Switch the immersion heater off at the wall and call us.
The seal has failed, or the element has corroded where it meets the cylinder. It needs attention soon, because water and mains terminals are close together.
The supply is isolated and the water turned off. Most elements sit below the water line, so the cylinder is drained, at least to below the element. The old element is unscrewed, which on an old copper cylinder takes care: a seized element can tear thin copper, and if we think that risk is high we tell you before we start. The new element goes in with a new seal, the cylinder is refilled and checked for leaks, and the element and thermostat are tested with the power back on.
On an unvented cylinder the same job means isolating a mains-pressure system and putting it back with its safety controls working, which is why it needs the G3 qualification.
In a Birmingham city centre flat we drained a Megaflo and replaced both elements, which came out coated in scale and corrosion. The case study has the photos.
Not every fault needs a new element. A thermostat can usually be replaced on its own without draining the cylinder. When an element has failed in a cylinder that has two, it is often worth changing both on the same visit: they are usually the same age, and the cylinder only has to be drained once.
An immersion heater is a part, and replacing it is normally all that is needed. We suggest replacing the cylinder only when it is leaking, when the copper is too thin to take a new element safely, or when it is the wrong size for the home. Other cylinder faults are covered on our hot water cylinder repairs page, and new cylinders on unvented cylinder installation and servicing.
If your hot water comes from a tall white unit in a flat, it may be a thermal store and not a cylinder: see PulsaCoil and thermal store repairs.
Synergy Gas & Plumbing is a family-run Birmingham business, trading since 2017 and led by Saeed Iqbal, an engineer with more than 20 years' experience, including ten years with British Gas (2006 to 2016). The company is Gas Safe registered, number 594385, and Saeed holds the G3 qualification for unvented hot water systems.
Replacing an immersion heater is plumbing and electrical work, not gas work, so Gas Safe registration is not the qualification that matters here, and it is not an electrical qualification. On an unvented cylinder the engineer must hold G3, and whoever does the job must be competent with the electrics.
A real job, written up with the photos we took on the day.
A tenant called with no hot water and asked for both immersion elements to be replaced. We drained the cylinder down, took out two scaled and corroded elements, fitted new ones and tested them. Hot water back the same visit.
Read the case studyPlease do not take the cap off the immersion heater. The terminals behind it are at mains voltage, and on an unvented cylinder the water behind them is at mains pressure.
| Job | Price |
|---|---|
| Diagnosis visit, Mon–Fri 8am–5.30pm | £99 |
| Immersion heater repair or replacement | Quoted after diagnosis |
| Outside office hours | Quoted by phone before we set off |
| Unvented cylinder annual service | £120 |
| Unvented cylinder service, bundled with a boiler service | £90 |
The £99 covers attendance and diagnosis in office hours (Mon–Fri 8am–5.30pm). It is not the price of an immersion heater repair: replacing an element or a thermostat is quoted and agreed before we start, and out-of-hours work is quoted by phone before we set off. No travel charge within 10 miles of B20 2JS; further out, £2 per mile may apply, agreed before booking. How our prices work.
Diagnosis £99
Diagnosis visit £99 in office hours. An immersion heater repair or replacement is quoted before we start.
No travel charge within 10 miles of B20 2JS. Further out, £2 per mile may apply — always agreed before anything is booked.
You cannot tell for certain without testing it with a meter, and that means working on mains wiring, which is not a job to do yourself. The signs are no hot water with the switch on, hot water that runs out after one shower, or a breaker that trips when the immersion heater is on. An engineer tests the element, the thermostat and the supply, and replaces only what has failed.
It is quoted for each job, not a fixed price. In office hours (Monday to Friday, 8am to 5.30pm) the diagnosis visit is £99. Once we have tested the element, the thermostat and the supply, and seen the cylinder, we give you a price for the repair before we start. Draining a large cylinder takes time, so the price depends on the cylinder as well as the part.
To change the element, yes, at least to below the level of the element. A thermostat can usually be changed without draining.
Usually the insulation inside the element has broken down, so current leaks to earth and the breaker trips, sometimes only once the element is hot. Leave it switched off and have it tested. Do not keep resetting it.
Often it makes sense. They are usually the same age, and the cylinder has to be drained to change the lower one, so doing both on one visit saves paying for a second drain-down later.
The job needs both skills: the element is plumbed into the cylinder and wired to the mains. On an unvented cylinder the engineer must also hold the G3 qualification. We do the draining, the element and the connection to it.
Scale is what wears elements out. Keep the thermostat at around 60°C and not turned right up, because hotter water lays down scale faster, and have an unvented cylinder serviced every year.
We cover Birmingham and the surrounding towns. Pick your area for local detail.
Unvented: £99 first hour in office hours. Vented or immersion: quoted after a £99 diagnosis
£120 annual service
£99 in office hours: diagnosis + first hour
Annual service £120
£99 in office hours: diagnosis + first hour
£99 (Mon–Fri 8am–5.30pm)
We will tell you honestly when we can get to you, and agree the price before any work goes ahead.
