Cylinder Immersion Heaters as Backup Hot Water
An immersion heater is an electric element fitted directly into a hot water cylinder, giving a way to heat water without the boiler running at all.
An immersion heater is an electric element fitted directly into a hot water cylinder, giving a way to heat water without the boiler running at all. Most cylinders keep one as a backup, and it's worth knowing it works before you actually need it during a boiler fault.
What it does
The element sits submerged in the cylinder's water and heats it directly via electric resistance, controlled by its own thermostat and time switch.
How it fails
Scale builds up around the element in hard water areas and it burns out, or the thermostat sticks and either stops it heating or lets water overheat.
Repair or replace
The element is unscrewed and replaced as a complete unit; the thermostat can sometimes be swapped separately if the element itself is sound.
Get your immersion heater checked
Tell us whether you've used the immersion heater recently and we'll test it works before you're relying on it during a boiler fault.
Questions we get asked
Is an immersion heater swap electrical work rather than gas work?
No, this is electrical and plumbing work, not gas work.
Can I replace an immersion element myself?
This involves draining the cylinder and working with an electrical element under water pressure, so we'd recommend having it done professionally.
Do all hot water cylinders come with an immersion heater fitted?
Most do as a backup, but not all — it's worth checking yours if you'd want the option during a boiler fault.