Immersion Heater Repair & Replacement

Professional immersion heater repair and replacement by qualified electricians. Faulty elements, thermostats, timer switches, and cylinder wiring. Qualified and insured.

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How it works

Symptom assessment and isolation

The electrician discusses the symptoms — no hot water, lukewarm water, tripping electrics, or timer not working. The immersion circuit is isolated at the consumer unit and the double-pole switch. The thermostat cover is removed from the top of the cylinder to access the wiring and controls.

Electrical testing

The electrician tests the immersion element for continuity (to check if it has failed open-circuit) and insulation resistance (to check for earth faults that cause tripping). The thermostat is tested for correct operation — checking that it switches the element on and off at the correct temperatures. The timer switch and wiring are tested for continuity and correct connection.

Component replacement

The faulty component is replaced. If the element has failed, the cylinder is drained (or a freeze kit is used), the old element is removed with an immersion spanner, and a new element is fitted with a new fibre washer. If the thermostat has failed, it is replaced and set to the correct temperature (typically 60°C). Timer switches are replaced at the wall position.

Refilling and testing

If the cylinder was drained, it is refilled and checked for leaks around the element seal. The circuit is re-energised and the immersion is tested for correct heating. The thermostat is verified to cut out at the set temperature. The timer switch cycle is confirmed. The circuit is re-tested for insulation resistance to confirm no faults.

What's included

Fault diagnosis and electrical testing

Continuity and insulation resistance testing of element

Thermostat testing and temperature calibration

Replacement of faulty immersion element (if required)

Replacement of faulty thermostat (if required)

Replacement of timer switch (if required)

Cylinder draining and refilling (if element replacement needed)

Leak check at element seal after refitting

Post-repair circuit testing

Thermostat set to recommended 60°C

Guidance on energy-efficient usage

What's involved

Immersion heater repair and replacement covers diagnosing and fixing faults with the electric heating element, thermostat, timer switch, and wiring of a hot water cylinder's immersion heater. Common problems include no hot water (failed element or thermostat), water too hot or not hot enough (thermostat fault), tripping electrics (element insulation breakdown), and timer not working (faulty timer switch or wiring). The electrician tests the immersion circuit, identifies the faulty component, and replaces it — restoring reliable hot water.

Immersion heaters operate at mains voltage (240V) and are typically on a dedicated 16A or 20A circuit with a double-pole isolator switch. The heating element is submerged in water inside the cylinder, making the combination of electricity and water particularly hazardous. A failing element can develop an earth fault that trips the RCD or, worse, makes the cylinder pipework live. Replacing an immersion element involves draining the cylinder, using a specialist element spanner, and making high-current electrical connections — work that requires both plumbing and electrical competence.

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Typical cost: £100–£300per repair

Every job is different — pricing depends on your property, location, and specific requirements. Describe what you need and a qualified electrician will quote you directly.

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How long does it take?

1-3 hours depending on the fault. Thermostat or timer replacement takes about an hour. Element replacement takes 2-3 hours including draining, fitting, and refilling the cylinder.

Regulations & safety

Safety notice

Always isolate the immersion heater at the double-pole switch and the consumer unit before any work. The element terminals inside the cylinder cover carry mains voltage and are in close proximity to water and metal pipework — contact is potentially fatal.

Never reduce the thermostat below 60°C to save energy. Water stored below 60°C can harbour Legionella bacteria, which causes Legionnaires' disease — a serious and sometimes fatal form of pneumonia.

If the immersion heater is repeatedly tripping the RCD or MCB, do not keep resetting it. A tripping element has an insulation fault that is leaking current to earth through the water. Continued use risks electric shock via the pipework and taps.

BS 7671:2018+A2:2022 (IET Wiring Regulations)

Immersion heater circuits must comply with BS 7671. The circuit requires a dedicated radial circuit with appropriate MCB/RCBO protection and a double-pole isolator switch adjacent to the cylinder. The wiring must be heat-resistant (typically 3-core flex rated for the element temperature) from the isolator to the element terminals.

Part P of the Building Regulations (Approved Document P)

Replacing an immersion element or thermostat on an existing circuit is generally non-notifiable maintenance work. However, if a new circuit needs to be run from the consumer unit (e.g., replacing an old radial circuit), this is notifiable under Part P.

HSE — Legionella and Water Temperature

Hot water must be stored at a minimum of 60°C to prevent Legionella bacteria growth, as recommended by the HSE Approved Code of Practice L8. The thermostat should be set to 60°C — not lower for energy saving, as this creates a health risk.

What to expect

The most common immersion heater fault is a failed element — the element burns out over time and the water stops heating. This is a straightforward replacement that takes 1-2 hours including draining and refilling the cylinder.

If the water gets dangerously hot (boiling or steaming from taps), the thermostat has failed in the closed position — the element runs continuously without cutting out. This is an urgent fault requiring immediate isolation and thermostat replacement.

Many cylinders have two immersion elements — an upper element for quick recovery (heats the top of the cylinder) and a lower element for full-cylinder heating. The upper element is used more frequently and fails first. The electrician will identify which element has failed.

Immersion timers allow you to heat water only when needed — typically for 1-2 hours before you need hot water. A basic segment timer costs £10-£20. Upgrading to a digital timer with boost button provides more flexible control and can reduce electricity bills.

If the immersion heater is the sole source of hot water (no boiler), consider the cylinder's age and condition. Cylinders over 15-20 years old may have internal corrosion. Replacing the element in a corroded cylinder may not be worthwhile — a new cylinder with a factory-fitted element is more reliable.

Having issues with your existing installation?

Already have a immersion heater repair & replacement and having issues? Check our troubleshooting guides.

RCD Keeps Tripping? Common Causes & How to Fix It (2026)

Your RCD keeps tripping and cutting power to multiple circuits. This guide covers every common cause — from faulty appliances and moisture to wiring faults and nuisance tripping — plus exactly what to do about it.

No Power In The Whole House

Your entire home has lost electricity. No lights, no sockets — everything is dead.

Frequently asked questions

We’re happy to answer all your questions.

How do I know if my immersion heater has failed?

The most obvious sign is no hot water when the immersion is switched on and sufficient time has passed (1-2 hours for a full cylinder). Check the double-pole switch is on, the timer is set correctly, and the circuit has not tripped at the consumer unit. If everything is on but the water is cold, the element or thermostat has likely failed.

Why does my immersion heater keep tripping the electrics?

A tripping immersion circuit almost always indicates the heating element has developed an insulation fault — the element's outer sheath has degraded, allowing current to leak through the water to earth. The RCD detects this earth leakage and trips to protect you. The element needs replacing — resetting the RCD without replacing the element will only result in it tripping again.

Can I replace an immersion heater element myself?

While technically possible, it involves working with mains electrical connections adjacent to a water-filled cylinder, using a specialist immersion spanner, and draining/refilling the cylinder without introducing air locks. The combination of electricity and water makes this a high-risk DIY task. We strongly recommend using a qualified electrician.

What temperature should the thermostat be set to?

60°C is the recommended temperature. This is high enough to kill Legionella bacteria (which multiply between 20-45°C) but not so high that it wastes excessive energy or creates a scalding risk at the taps. If you have young children or vulnerable adults, consider fitting a thermostatic mixing valve at the outlets to limit the delivery temperature to 43°C.

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