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Immersion heater not working? What to check.
No hot water from the immersion: the switch, timer and fuse board checks, the signs of a failed element, and when to call us.
No hot water and the immersion heater’s on? Before you call anyone, there are a few things worth checking.
Quick checks
- The switch. Immersion switches are usually near the cylinder, often with a red light. Some have a Sink / Bath switch for two elements: try the other one.
- The timer. Many immersions run on a timer or Economy 7. Check the time is right (after a power cut or clock change) and the boost button works.
- The fuse board. Look for a tripped breaker or RCD for the immersion. If it trips again when switched on, the element has probably failed.
- The fused spur. Some immersions are fed through a switch with a fuse. A blown fuse can mean a failed element.
Common causes
| Symptom | Likely cause |
|---|---|
| No hot water, switch light on | Failed element or tripped thermostat cut-out |
| Trips the RCD or breaker when switched on | Failed element leaking to earth |
| Water only lukewarm | Thermostat set too low or faulty; one element of two failed |
| Water too hot or scalding | Failed thermostat. Switch off and call us |
| Burning smell or scorched switch | Overheating connection. Switch off and call us |
Elements and thermostats are replaceable parts. Replacing an element means draining the cylinder, so it’s a job for an electrician or plumber, and we check the circuit and switch while we’re there.
Unvented (pressurised) cylinders
If your cylinder is unvented (a sealed system, usually with a pressure relief valve, expansion vessel and no tank in the loft), work on it should only be done by someone qualified for unvented systems. Tell us when you call, and we’ll make sure the right engineer comes.
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Questions we’re asked
Why is my immersion heater not working?
Check the switch, the timer or Economy 7 setting, and the fuse board. If the circuit trips when you switch it on, or there is power but no heat, the element or thermostat has usually failed.
How do I know if my immersion element has gone?
The usual signs are no hot water with the switch on, or the RCD tripping as soon as you switch the immersion on. An electrician can confirm it with a quick test.
Does my immersion heater have a reset button?
Many immersion thermostats have a safety cut-out with a small reset button under the cover. It operates if the water gets too hot. Don’t take the cover off yourself; it is live. If it keeps tripping, the thermostat needs replacing.
Can an immersion heater element be replaced?
Yes. It means draining the cylinder and fitting a new element and usually a new thermostat. On unvented cylinders it must be done by someone qualified for unvented systems.
Written by SEGplc. Last updated 19 October 2026.
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