• Richard Gross

How do I use my immersion heater?

Updated: May 19, 2020

How to use your immersion heater depends on what type of hot water system you have. Here, we break down how to use immersion heaters for the different types of system.

How do I use my Immersion Heater?

There are numerous types of boilers and heating systems, so how you use your immersion heater will depend on which system you have (find our guide to the different types of heating system here).

If you have a gas boiler and separate hot water cylinder, then the boiler will usually heat the hot water for you. In this scenario, the immersion heater is only required as an emergency back up to heat the water in the event of a boiler failure.

If you have a fully electric heating system (for example: storage or panel heaters), then it is likely that your hot water is heated using an immersion heater. The hot water cylinders installed on these systems are what is known as direct cylinders. This is because they are heated by the immersion heaters transferring heat directly into the hot water.

These systems will typically have two immersion heaters installed in the side of the hot water cylinder. Each immersion will be wired into a switch or timer on the wall adjacent to it, where they can be turned on and off to heat the water as required.

How long does it take for the immersion heater to work?

The time it takes to heat a hot water cylinder varies depending on the size of the cylinder and number of immersion heaters. We would typically recommend switching the immersion heater on around two hours before you intend to use the hot water to give it time to heat the cylinder. Many of these systems will use ‘Economy 7’ electricity tariffs and, as such, will have an on-peak and off-peak immersion heater.

The off-peak immersion heater will be the one lower down the cylinder and should be left on all the time when hot water is required. The off-peak immersion will automatically use cheaper electricity over night to heat the water. The on-peak immersion can be used anytime but should only be turned on during the day to re-heat the water if the store of water has been exhausted.

If you find that your water is not being heated overnight, or that you cannot reheat it during the day with the on-peak immersion, then you should contact a heating engineer to investigate this issue.

Got more plumbing questions? Read through our FAQs here, or give our expert engineers a call to find out how we can help you.