How to Change an Immersion Heater

Firstly watch the brief instructional video below on how to change an immersion heater. That will probably cover most points. If you have any more problems scroll further down the page to our instructional guide.

The immersion heater is the heating element that is situated in your hot water tank. It is easy to identify. The exposed part looks like an upturned cup and can be found at the top of the tank (top entry) or at the side of the tank (side entry).

In most households the hot water is also heated via a heating coil from the boiler with the immersion just a back up. In houses with economy 7 or 10 electrical heating the immersion is the only way to heat your hot water.

Regardless of system, the immersion heater is an important component and should be changed as soon as it fails.



How do I know my immersion heater has failed?

  1. Is your hot water hot? It may sound obvious but test whether it is still hot. In houses where there is a hot water coil from the boiler, turn the boiler off.

  2. Does the Immersion heater have an electrical supply? Always use a qualified electrician for this bit. Remove the cover on the immersion, usually a single screw and test the electrical supply. The live supply will go through a thermostat. Test both sides of the thermostat, it may be faulty and can be changed without having to replace the whole immersion heater. If you find there is no electrical supply, check fuses and breakers up to the immersion.


If you have none of the above then your immersion heater will need changing. If you want to know how to change an immersion heater then watch this brief video:

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How to change the immersion heater

  1. Turn the immersion off electrically and remove any fuses just in case. Remove all the wires and make a note of live, neutral and earth.

  2. Identify the cold water supply to the hot water tank and turn it off. Sometimes you will have to go up in the loft and drain the supply tank.

  3. Open the hot water taps until the water stops. Sometimes on a pressurised system this can take 10 minutes or more. Tip: The tank is still not drained but now is the time to LOOSEN the immersion heater. The water still inside the immersion tank stabilizes the thin copper wall from the pressure you apply to remove the heater. After this close the cold water supply valve to the tank.

  4. Identify the drain point at the bottom of the tank and using a hose, drain the tank.

  5. When the tank is drained, fully unwind the immersion heater. Tip: The new Immersion heater should be supplied with a fibre seal. Smear this with jointing paste and apply to the immersion heater.

  6. Insert the new heater, careful not to cross the thread. Tighten but not too much.

  7. Turn off the drain point and taps. Re-fill the tank. Test for leaks.

  8. Re-install the electrical connections and set the thermostat in the immersion to the desired temperature (55 degrees Celsius). Replace cover, any fuses and turn on the power. After 30 minutes turn on the hot tap. You should notice the water start to warm. It may take 4-5 hours before you get really hot water.