What is this?
An immersion heater is an electric element fitted inside your hot water cylinder (tank). It heats the water directly, providing domestic hot water for baths, showers, and taps. When it stops working, you have no hot water from the tank. Immersion heaters are common in homes with no combi boiler and as a backup in homes with a gas boiler.
Common causes
- Thermostat on the immersion has tripped or failed
- Heating element has burned out — common in hard water areas
- Blown fuse in the spur or consumer unit MCB tripped
- Loose or corroded wiring connections at the immersion heater
- Timer or programmer not set correctly
- High-limit safety cutout has tripped
Is it dangerous?
An immersion heater that has simply stopped working is not immediately dangerous. However, if the wiring connections are corroded or the element is leaking, there is a risk of electric shock near the hot water cylinder. Do not attempt to remove or inspect the immersion heater yourself.
Can I fix it myself?
Check the consumer unit for a tripped MCB or RCD. Check the spur switch near the hot water cylinder is on. Check the timer or boost switch. Some immersion heaters have a red reset button on the thermostat — press it once. If it trips again, the thermostat or element is faulty.
When to call an electrician
Call an electrician if the reset button trips again after pressing, if the MCB or RCD trips when the immersion is turned on, if the immersion heater is very old and you suspect element failure, or if there is any sign of water around the electrical connections.
What will an electrician do?
Test the supply to the immersion heater
Check the thermostat and high-limit cutout
Test the element for continuity and insulation resistance
Inspect wiring connections for corrosion or damage
Replace the element and/or thermostat if faulty
Test the repaired system and set the thermostat to the correct temperature (usually 60°C)
Typical cost
£100 – £280
Element and thermostat replacement is the most common repair. Costs include draining the cylinder. Hard water areas may need more frequent element replacement.
