An immersion heater stops working and you have no hot water. You can shower from the boiler, but the tank isn’t heating. The immersion heater has failed.
An immersion heater is a simple device: an electric heating element in a hot water tank. When it fails, there’s no backup if your boiler breaks or is off for maintenance. It’s also cheaper to fix than you might think.
How an immersion heater works
An immersion heater is a metal rod with an electric heating element inside. It screws into the side or top of your hot water tank. When powered on, it heats the water in the tank directly, independent of your boiler.
Most homes have one. Some have two (an upper and lower element). In smaller flats or homes without space for a full heating system, it’s the primary heat source.
Why an immersion heater fails
The heating element inside corrodes. Scale builds up on it from minerals in hard water. Water leaks in through the seal where the element meets the tank. These all mean the element stops conducting heat.
The thermostat dies. It controls when the element switches on and off. When it fails, the element either won’t turn on or stays on constantly, wasting electricity.
The timer breaks. If your immersion heater is set to turn on at certain times, the timer can fail, leaving the heater always off.
The switch fails. A physical switch controls power to the element. When it wears out, power doesn’t reach the heater.
Signs your immersion heater isn’t working
The water doesn’t heat at all. You’ve waited an hour with it switched on. Nothing. It’s either completely dead or the element is broken.
The water heats very slowly. Instead of one or two hours to a full tank, it takes four or five. The element is weakening. It still works but at reduced efficiency.
The timer doesn’t turn it on at the scheduled time. You set it to heat overnight but find it cold in the morning. The timer is failing.
There’s a smell when you turn it on. A burning smell means the heating element is struggling, overheating, or failing internally.
You see water dripping from where the immersion heater screws into the tank. The seal has failed. You have a leak.
Can you repair it yourself
You can replace the immersion heater element yourself if you’re confident with basic plumbing. The element unscrews from the tank. Drain the tank first. Unscrew the old element and screw in a new one (cost: GBP 20-40). Turn the power back on.
If you’re not comfortable doing this, a plumber can replace it in 30 minutes to one hour. Cost: GBP 100-200 including parts.
Don’t attempt to repair the thermostat or timer yourself. These are electrical and need an electrician or qualified heating engineer.
FAQs
How long does an immersion heater last?
Usually 10-15 years. In hard water areas, scaling shortens this to 8-10 years. Poor maintenance (no servicing) reduces lifespan further.
Can you use your home without an immersion heater?
If your boiler works, yes. The boiler heats the tank. The immersion heater is backup or used when the boiler is off. Without both, you have no heat.
What does a plumber or electrician fix an immersion heater?
A plumber handles the element and tank connection. An electrician handles the timer and thermostat wiring. Complicated faults need a heating engineer (who has both skills).
Is it cheaper to replace or repair the immersion heater?
Usually cheaper to replace the element (GBP 100-200). If the tank connection is damaged, it might be worth replacing the whole assembly (GBP 200-400). Tank replacement (GBP 1,000+) is only needed if the tank itself has corroded.
