Replace an immersion heater

Trade: Heating Engineer

⭐ Introduction

An immersion heater is an electric heating element that’s installed inside a hot water cylinder (usually a copper or unvented cylinder) to heat water when your main boiler isn’t in use or as a backup. Replacing an immersion heater may be necessary if it’s no longer heating water effectively, has corroded, or stopped working entirely.

Typically, an immersion heater lasts around 10–15 years, although hard water areas or scale build-up can reduce its lifespan. Knowing when to replace the immersion heater can save you from having no hot water or risking damage to your cylinder.

🔧 What the job involves

Replacing an immersion heater involves removing the old heating element from your hot water cylinder and installing a new one. The process includes:

Turning off the electricity supply, usually at the consumer unit (fuse box), to ensure safe working.
Draining sufficient water from the cylinder to access and remove the old immersion heater.
Unscrewing or unbolting the old element from the cylinder.
Fitting and sealing the new immersion heater in the same location.
Reconnecting the electrical wiring correctly.
Refilling the cylinder and restoring the electrical power.
Testing the heater to ensure it’s working safely and heating water effectively.

Since the work involves electricity and water, as well as access to your cylinder (which may be in a loft, airing cupboard, or cupboard), it’s essential to use a qualified Heating Engineer. They will ensure the replacement complies with Building Regulations and Part P electrical safety standards.

📝 Step-by-step from booking to completion

Enquiry: Contact a Gas Safe registered heating engineer or accredited electrician with experience in immersion heaters. Provide details about your hot water cylinder and symptoms.
Survey and Quote: The engineer may arrange a visit to inspect your cylinder, check access, and confirm the type of immersion heater required. They will then provide a written quote including parts, labour, and any additional costs.
Scheduling: Agree a date for the replacement. Good engineers will offer a time window and confirm when they’re en route.
Day of works: The engineer arrives, confirms your requirements, isolates the electrical supply and water if necessary, and carries out the replacement safely.
Testing and commissioning: Once fitted, they test the immersion heater, check for leaks and ensure the electrical installation is safe.
Advice and paperwork: You’ll receive safety advice, any relevant certification (such as electrical work certification under Part P if required), and an invoice.
Aftercare: Keep details of your replacement and schedule regular servicing of your cylinder and heating system.

💷 Main costs to expect

Labour: Typically £80-£120 per hour, depending on region and engineer experience.
Immersion heater unit: Usually £30–£70 depending on size (e.g. 2kW or 3kW) and brand.
Parts and materials: Including sealing gaskets, wiring accessories, and possibly a new thermostat or timer (£20–£50).
Disposal: Some engineers include this; others may charge a small fee (~£10) to dispose of the old element responsibly.
Certification: If electrical work requires notification under Part P, expect a small fee (~£30–£50) for certification or notification to Building Control.

Example itemisation:

Labour (2 hours): £180
Immersion heater element: £50
Materials (gasket and wiring): £30
Disposal: £10
Certification: £40
Total (ex VAT): £310

Remember, VAT at 20% is usually added unless exempt.

📊 What affects the price

Access: If the cylinder is difficult to reach (e.g. in lofts or confined spaces), labour time and complexity increase.
Cylinder type and size: Larger or unvented systems may need a specific element or additional work.
Electrical connection: Older wiring or installations may require upgrades to meet Part P compliance and Building Regulations.
Remedial works: If corrosion or leaks are found, extra repairs may be needed.
Location: Prices vary between regions — London and the South East are typically higher than other UK areas.
Timeline: Emergency or out-of-hours calls usually incur higher costs.

⏱ How long does it take?

A straightforward replacement of an immersion heater typically takes 1 to 3 hours, depending on:

Ease of access to the cylinder.
Whether the cylinder needs full or partial draining.
Complexity of the wiring.

If extra repairs or electrical upgrades are needed, the job can take up to a full day.

🏠 Can you DIY it?

Replacing an immersion heater involves working with electricity and water, which can be dangerous if not done correctly. In the UK, immersion heaters must comply with Part P electrical regulations, meaning electrical work should be:

Carried out by a qualified electrician or registered Heating Engineer.
Inspected or certified to ensure safety.

DIY replacement is not recommended, particularly because:

Incorrect electrical reconnection can cause shocks or fire hazards.
Poor sealing can cause water leaks, damaging your property.
You may invalidate insurance or warranties.

Always hire a professional to ensure safety and compliance.

💰 Typical UK price range

The typical total cost to replace an immersion heater ranges from approximately £250 to £450 + VAT (20%), depending on the factors outlined above.

This estimate includes parts, labour, and basic certification but may rise if your installation is complex or requires additional repairs.

✅ Handy tips before you start

Check your cylinder type: Know if you have a vented or unvented system, and the size, to help your engineer find the right replacement.
Clear access: Make sure any cupboards or loft spaces are tidy and accessible.
Turn off power: For safety, ensure you can isolate power at the consumer unit if you notice issues before the engineer arrives.
Ask about certification: Confirm your engineer is qualified and that you’ll receive proof of safe electrical work.
Keep paperwork: Store all invoices, certificates, and manuals for future reference or warranty claims.
Regular servicing: Schedule annual checks of your hot water system to catch problems early and prolong system life.

Replacing an immersion heater is straightforward with the right professional help, ensuring your home stays warm with reliable hot water.