The practical no frills guide.

Immersion heater

Yes, it’s that time. Again. You’re excited, and that hot shower you’ve been looking forward to is just minutes away.

Turning the shower dial, you wait for that torrent of warmed water and the total relaxation that comes with it. But the monsoon doesn’t appear. And your mood and day right there and then fall flat as a pancake.

At this point your thoughts turn to the immersion heater and why the XXXX it’s not working!

The straight-up answer is that the perpetrator may be anything from limescale build-up to damaged elements or even a faulty thermostat.

Like any appliance, immersion heaters can encounter issues that affect their performance. Instead of immediately considering a replacement, understanding how to troubleshoot and repair common immersion heater problems can save you both time and money.

So, it’s time to find out why your immersion heater’s not giving the goods and how you can sort it out.
In the no-frills mastering guide to immersion heater repair, we’ll delve into the intricacies of immersion heaters, explore common issues, and provide step-by-step instructions for troubleshooting and repair.

Before undertaking any/all plumbing, heating or related work you should always take your own independent professional advice.

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Plumber - Paul

Paul's a member of the Chartered Institute of Plumbing & Heating Engineers, Water Regs UK (formerley WRAS – Water Regulations Advsiory Scheme) certificated as well as a qualified unvented cylinder engineer and a qualified heat pump engineer.

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What’s an immersion heater and how does it work?

In your hot water cylinder you’ll find an electric water heater – an immersion heater inside.

It works just like a kettle and uses a large metal loop – an electric resistance heater to heat the water around it. Controlling the water temperature’s either, an internal or external thermostat.

So, whenever you turn a tap on, a high-pressure stream of fresh cold, water goes into the tank and pushes the heated water upwards and out to your shower, bath or sink.

As for the wiring, typically immersion heaters are connected to your central electrical supply. The best part is that an immersion heater can be turned on and off which means that you don’t have to spend money keeping a whole cylinder of water ready and waiting to use.

Components of an immersion heater

Heating element. The part responsible for heating the water.

Thermostat. Regulates the water temperature.

Immersion tube. Protects the heating element.

Control switch. Manages the heater’s operation.

Types of immersion heater

Incoloy immersion heaters. Resistant to corrosion and well-suited for hard water areas.

Copper immersion heaters. Efficient heat transfer but may be prone to corrosion.

Titanium immersion heater. Highly resistant to corrosion, suitable for aggressive water conditions.

5 Common immersion heater issues and DIY solutions

No hot water

Possible causes

Faulty heating element

Tripped thermostat

DIY repair

Check for a tripped circuit breaker or blown fuse

Test the heating element with a multimeter

Replace the heating element if faulty

Reset or replace the thermostat if necessary

Water not getting hot enough

Possible causes

 Incorrect thermostat setting

Lime scale build up on the heating element

DIY repair

Adjust the thermostat setting to the desired temperature

Descale the heating element using a suitable descaling solution

Strange noises from the immersion heater

Possible causes

Sediment build up in the tank

DIY repair

Drain and flush the water heater to remove sediment

Install a sediment filter to prevent future build up

Leaking water from the immersion heater

Possible causes

Corrosion on the immersion tube

Faulty gasket or washer

DIY repair

Inspect the immersion tube for corrosion and replace if necessary

Replace the gasket or washer at the leaking point

Tripped circuit breaker or blown fuse

Possible causes

Electrical overload or a short circuit

DIY repair

Identify the cause of the overload or short circuit

Reset the circuit breaker or replace the blown fuse

Immersion heater repair - step-by-step

Turn off the power

Before starting any repair work, turn off the power supply to the immersion heater at the circuit breaker.

Inspect for visible issues

Check for obvious issues like loose wires, visible damage, or signs of water leakage.

Check the circuit breaker

If the immersion heater is not working, check the circuit breaker or fuse box for tripped breakers or blown fuses.

Test the thermostat

Use a multimeter to test the thermostat for continuity.

Adjust the thermostat setting to ensure it matches your desired water temperature.

Inspect the heating element

Test the heating element with a multimeter to ensure it is functioning.

Replace the heating element if it shows no continuity.

Descale the heating element

If water is not heating adequately, descale the heating element using a suitable descaling solution.

Drain and flush the tank

If there are strange noises or sediment build up, drain and flush the water heater tank.

Consider installing a sediment filter to prevent future build up.

Inspect and replace gaskets/washers

If there is water leakage, inspect gaskets and washers for damage.

Replace any damaged gaskets or washers.

Inspect the immersion tube

Check the immersion tube for signs of corrosion.

Replace the immersion tube if corrosion is present.

Reset or replace the thermostat

If the thermostat is faulty, reset or replace it according to the manufacturer’s instructions.

Turn on the power

Once repairs are complete, turn the power back on and monitor the heater’s performance.

5 Preventive maintenance tips

Regularly descale the heating element

Periodically descale the heating element to maintain efficiency.

Adjust thermostat settings

Ensure the thermostat is set to the desired temperature to prevent overheating or insufficient heating.

Install a sediment filter

Reduce sediment build up by installing a sediment filter in the water heater.

Inspect for leaks

Regularly check for signs of water leakage around the immersion heater.

Professional servicing

Schedule professional servicing periodically to ensure the longevity of the immersion heater.


With the knowledge gained from the no frills mastering guide to immersion heater repair, you can troubleshoot and repair common issues with your immersion heater.

Regular maintenance and seeing to any problems quickly will not only extend the lifespan of your immersion heater but also ensure a reliable supply of hot water for your household needs.

Remember, if you encounter complex issues or feel uncertain about any repair process, ask a qualified professional.

And if you’d like some help fixing your immersion heater or installing a new one, from our local Caversham plumbers near me, we’d be pleased to. We’re only a phone call, text, WhatsAp or email away!

(Caversham’s #1 plumbers)


Our mastering series and blog are provided on an “as is” basis, in good faith and subject to change without notice. All reasonable efforts have been made to ensure its accuracy. However, this isn’t warrantied, and liability isn’t accepted for any damage or loss whether direct, indirect, special or consequential suffered by anyone in accessing, downloading, using or relying on it.

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