Replacing a back boiler: what the job involves and how ECO4 can help

By ApplyFreeBoiler.uk (Reliant Energy Solutions Ltd), an ECO4 heating and insulation installer based in Bury, Greater Manchester. We are not the government, Ofgem, your council or an energy supplier.

A back boiler is a boiler built into a fireplace, usually behind a gas fire, inside the chimney breast. They were a common way to heat UK homes for decades, and many are still running. If you have one and are thinking about replacing it, this guide explains what is involved and how ECO4 may help.

Are back boilers still allowed?

Yes. You can keep using a back boiler as long as it works safely and is serviced regularly by a Gas Safe registered engineer. What changed is the standard for new boilers. Building Regulations in England changed in 2005 to expect new gas boilers to be high-efficiency condensing models, which is why back boilers stopped being fitted as standard.

How to tell if you have one

• You have a gas fire or solid fuel fire in the chimney breast and cannot find a boiler anywhere else.
• You have a hot water cylinder, usually in an airing cupboard, and often a cold water tank in the loft.
• Pipes run from the fireplace towards the cylinder or radiators.

If you are unsure, an engineer can confirm it during a service or survey.

Why people replace them

Most back boilers still in use are now quite old. In many homes the back boiler is the whole heating system, so a single fault can leave you without heating and hot water. Parts can be harder to find, and older models are typically much less efficient than a modern condensing boiler.

What the replacement involves

Replacing a back boiler is more than a like-for-like swap:

1. Removal. The old boiler and fire unit are disconnected and removed, and the gas supply to them is made safe.
2. The fireplace. The opening is usually sealed or made good. Some households choose a new fire; others close it off.
3. The new boiler location. A new condensing boiler is normally fitted elsewhere, often a kitchen or utility room, with its own flue through an outside wall or roof.
4. Pipework. New pipework connects the boiler to the existing radiators and, where kept, the hot water cylinder.
5. Hot water choice. Depending on the home, you might move to a combi boiler and remove the cylinder and loft tank, or keep a cylinder with a system or regular boiler.
6. Controls. A programmer, room thermostat and radiator valves are usually fitted with the new system.

Expect the work to take longer than a standard boiler swap, with some disruption around the fireplace and wherever the new boiler goes.

How ECO4 can help

Under ECO4, back boiler replacement may be funded where the household qualifies, usually through a qualifying benefit or a council LA Flex route, and the home meets the scheme rules. Owner-occupied homes are usually considered if rated EPC D to G. A survey decides what can be funded, and insulation may be recommended first.

Eligibility does not guarantee a measure, and Ofgem notes that contributions can apply in some cases. Ask for anything you are being asked to pay in writing before you agree. Be wary of anyone who asks for a fee just to apply. ECO4 is due to end on 31 December 2026.

Questions to ask your installer

• Where will the new boiler and flue go?
• What happens to the fireplace and chimney?
• Will I keep my hot water cylinder?
• Which controls will be fitted?
• Is the engineer Gas Safe registered, and can I check their ID card?

Learn more

ApplyFreeBoiler.uk has a detailed guide to back boiler replacement under ECO4. You can also apply through an obligated energy supplier or your local council via GOV.UK.

Published by ApplyFreeBoiler.uk, run by Reliant Energy Solutions Ltd (company no. 16100301), Bury, Greater Manchester.