Immersion Heater Not Working – Find Out Why and What to Do

It’s that time again – you’re ready for that hot shower you’ve been waiting for all day. You turn on the tap, expecting a steady stream of hot water, only to be met with an unpleasant blast of cold.

If your immersion heater is not working, the cause could be anything from a faulty thermostat, a blown fuse, or a tripped circuit breaker, to limescale buildup or even a burned-out heating element. In some cases, the issue may be as simple as pressing the reset button, while in others, you might need to call an emergency plumber.

Many homeowners also report that their immersion heater keeps tripping the fuse board, which often points to wiring or insulation issues. And since immersion heaters typically have a lifespan of 5–10 years (with many manufacturers offering a 5-year warranty), age can also be a factor.

In this guide, we’ll explain the most common immersion heater problems, troubleshooting steps you can try yourself, and when to call for immersion heater repair.

What Is an Immersion Heater?

An immersion heater is an electric heating device fitted inside a hot water cylinder. It consists of a heating element, thermostat, and wiring connected to the mains. The heating element warms the water, while the thermostat regulates the temperature. Unlike gas boilers that use burners, immersion heaters rely solely on electricity.

They are popular in UK homes without gas supply or as a backup hot water heaters option. Modern cylinders often have more than one immersion heater, typically a lower element for daily heating and a top element for “boost” functions, giving you a quick supply of hot water when needed.

How Does an Immersion Heater Work

An immersion heater works by passing a steady flow of electricity through its heating element, which warms the water directly inside your hot water cylinder. A built-in thermostat—either internal or external—regulates the temperature to keep your water ready for use. If the immersion heater thermostat is not working, however, you may notice water that is either lukewarm or scalding hot, one of the first signs of a fault.

When you turn on a tap, fresh cold water enters the tank under pressure and pushes the heated water out, ensuring a consistent supply. Once heated, the hot water naturally rises to the top of the cylinder, closest to the element, while cooler water remains at the bottom until reheated.

In terms of wiring, immersion heaters are usually connected directly to your home’s central electrical supply through an isolating switch. Some models include an indicator light, which shows when the heater is operating. If this immersion heater light is not working, it could point to a blown bulb, a faulty switch, or a more serious electrical issue. For energy savings, you can turn the immersion heater on and off as needed rather than leaving it running constantly.

How Do I Know if My Immersion Heater Is Working?

If you suspect your immersion heater isn’t heating properly, there are a few simple checks you can do before calling a professional:

• Check the power supply – Make sure the immersion heater is connected and the isolator switch is turned on. If it’s on its own circuit, check the breaker hasn’t tripped.
• Look at the indicator light – Many units have a small light that glows when the heater is running. If the immersion heater light is not working, it might point to a blown fuse, a faulty bulb, or a deeper wiring issue.
• Listen for a gentle hum – A working heating element often makes a faint humming sound while heating. Total silence may indicate the unit isn’t drawing power.
• Check the thermostat – If the thermostat isn’t set high enough (at least 55°C in the UK to prevent legionella bacteria), the water may stay lukewarm.
• Test the water temperature – After leaving the heater on for 30–60 minutes, run a hot tap. If the water hasn’t warmed, it’s a clear sign of a fault.

If you’ve run these checks and still aren’t sure, it’s safest to arrange an immersion heater repair with a qualified heating engineer. They’ll diagnose whether it’s a thermostat, fuse, or heating element problem.

Common Immersion Heater Problems and Solutions

Now that you know how the unit works, it’s time to look at the most common issues that lead to an immersion heater not working. By the end of this section, you’ll know how to carry out a basic immersion heater fault diagnosis and when to call for professional help.

The Circuit Breaker Has Tripped

If your immersion heater is not working and there’s no hot water, one of the most common reasons is a tripped breaker or a blown fuse. Immersion heaters draw a lot of power, and when the circuit is overloaded, the breaker shuts off to prevent overheating or even an electrical fire.

Solution:
First, check your main electrical panel to see if the immersion heater fuse keeps blowing or the breaker has tripped. Simply switch it off and then back on again. If the immersion heater keeps tripping after a reset, this usually points to a deeper issue such as a faulty immersion element or thermostat problems.

Safety tip: Immersion heaters run on 220–240 volts. Never touch wiring unless the power is completely switched off. If you’re not confident, it’s safer to book an immersion heater repair service in London and let a professional handle the fault. They can test the immersion heater reset button location, inspect the wiring, and replace faulty components quickly.

If you keep experiencing a tripped breaker or blown fuse, don’t ignore it. Apart from leaving you with no hot water, repeated failures may shorten your immersion heater lifespan. In some cases, replacing the thermostat or the heating element is cheaper in the long run than repeated call-outs.

You Have a Faulty Thermostat

Another common reason your immersion heater is not working properly is a thermostat fault. When this happens, your water may suddenly stop heating or come out scalding hot, because the immersion heater thermostat is not working as it should.

Solution:
Start with a reset. If you have a modern immersion heater with an external thermostat, you’ll usually find a clearly marked immersion heater reset button (UK models often feature a red safety switch). Pressing this button can sometimes get things working again.

For older heaters, follow these steps:

• Cut the power at the circuit breaker to avoid any risk of shock.
• Remove the lid that protects the upper heating element.
• Carefully take off the safety cap without touching wires.
• Locate and press the small reset button – some models require a pin or narrow tool to reach it.
• Reassemble the cover securely, switch the power back on, and test the heater.

If the thermostat won’t reset, or if the immersion heater keeps tripping after you restart it, the component is most likely burnt out and needs replacing. At this point, it’s best to book a professional heating specialist. They can safely test the immersion heater thermostat, replace faulty parts, and make sure your system is running efficiently again.

Immersion Heater Not Heating Water Enough (Lukewarm Water)

In some cases, the heater doesn’t stop working entirely but only produces lukewarm water. This can be just as inconvenient as no hot water at all.

Common causes include:

• The thermostat set too low – should be at least 55°C in the UK for safe and hot water.
• Limescale buildup – coating the element and reducing efficiency.
• Weak or aging element – still heats, but not enough for the whole tank.
• Electrical supply issues – such as a blown immersion heater fuse or faulty wiring.

Solution:
First, check and adjust the thermostat setting. If it’s correct but water still isn’t hot enough, press the reset button and confirm the fuse hasn’t blown. If the problem persists, it’s usually down to limescale or a worn element—both of which require professional repair or replacement.

A Damaged Immersion Element

Another common reason why an immersion heater stops working is a faulty or burned-out heating element. This usually happens after years of use, when rust, corrosion, or limescale buildup weaken the element until it can no longer heat properly.

Signs your immersion heater element is failing include:

• Water takes far too long to heat (a 150-litre cylinder should heat in about 1–3 hours under normal conditions).
• The heater warms water unevenly or overheats despite the thermostat setting.
• The unit keeps tripping the circuit breaker or blowing a fuse.
• Strange hissing or popping noises coming from the cylinder.

Solution:
If you suspect the heating element is the problem, you can do a basic check: switch off the power, remove the cover, and test the element with a multimeter to see if it’s conducting electricity. If it fails the continuity test, the element needs replacing.

Replacing an immersion heater element involves draining the cylinder, removing the old element with a special spanner, and carefully installing a new one. Because this requires both plumbing and electrical expertise, and risks damaging the tank if done incorrectly—it’s best to arrange a professional immersion heater repair service. A qualified engineer can safely fit a replacement element and restore hot water quickly.

Limescale Buildup

If you live in a hard water area, limescale can build up quickly inside your hot water cylinder. Over time, mineral deposits coat the immersion heater element, reducing its efficiency and in some cases causing the immersion heater thermostat to stop working. This not only shortens the heater’s lifespan but can also leave you with lukewarm water or frequent trips of the immersion heater fuse.

Signs of limescale problems include:

• Hot water takes much longer to heat.
• Strange noises like hissing, banging, or popping when the element is on.
• The immersion heater keeps tripping the breaker as the element overheats.

Solution:
To reduce limescale buildup:

• Install a water softener installation or limescale filter to stop deposits from forming in the first place.
• Ask a plumber to flush the immersion heater and cylinder with a high-pressure water jet if scale is already present.
• For prevention, you can also use a descaling solution approved for hot water systems.

We recommend that you avoid disassembling your immersion heater if you lack the required expertise to do so!

Problems with the Insulation

When your immersion heater suffers from insulation breakdown, the electrical current flow to the heating element can be disrupted. This often leads to overheating, blown fuses, or the immersion heater keeps tripping the main breaker. Another sign may be the immersion heater light not working, making it harder to tell if power is reaching the unit.

Common warning signs:

• Frequent fuse blows or breaker trips.
• Buzzing noises, burning smells, or scorch marks near the cap.
• Water that heats inconsistently – either too hot or not heating at all.

Solution:
Unlike pressing the immersion heater reset button UK on a thermostat, insulation faults affect the wiring and internal safety features. These are not DIY-friendly fixes. Attempting them without the right training carries a serious risk of electric shock.

Preventive Maintenance Tips for Immersion Heaters

Like any appliance, immersion heaters last longer with care. Here’s how to extend their life:

• Regularly flush the tank – Draining out sediment build-up prevents blockages and improves heating efficiency.
• Fit a limescale filter – In hard water areas, installing a softener or filter will protect the element.
• Check for corrosion – Inspect the tank and element for rust or wear.
• Test the pressure relief valve – Ensures your cylinder doesn’t over-pressurise.
• Book annual servicing – A plumber can spot wiring problems, insulation issues, or signs of element damage early.

A well-maintained immersion heater not only reduces the risk of breakdowns but also lowers your electricity bills.

Takeaways

Immersion heaters are a reliable alternative if your home doesn’t have a gas supply, but like any appliance, they can develop faults over time. The most common reasons for an immersion heater not working include:

• Burned or faulty internal parts, such as a heating element or thermostat (sometimes requiring an immersion heater reset button to be pressed).
• Electrical problems like a tripped circuit breaker, blown fuse, or the immersion heater light not working, which may signal a wiring fault.
• Limescale buildup in hard water areas, which can shorten the lifespan of the unit and reduce efficiency.
• Insulation or wiring breakdowns that can cause the heater to trip repeatedly (immersion heater keeps tripping).

If you’re dealing with recurring problems, it may be time to book an immersion heater repair with a qualified plumber or heating engineer. Regular maintenance and preventative steps, such as installing a limescale filter or flushing the cylinder, can extend the life of your heater and keep hot water flowing reliably.

Immersion Heater Not Working – Find Out Why and What to Do

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