Back boiler replacement: your options explained

What a back boiler is

A back boiler sits behind a gas fire, feeding a cylinder and tanks. They were fitted in their thousands from the 1960s to the 1980s — and if yours is still running, it is older than most cars on the road and far less efficient than anything made this century.

Your replacement options

• Combi conversion — the most popular: back boiler, fire, cylinder and tanks all come out; one wall-hung combi replaces everything
• System boiler — keeps the cylinder if several bathrooms run at once
• Heat-only swap — rare; only where the existing cylinder and tanks are staying

What the job involves

A back boiler conversion is one of the bigger jobs: the fire surround often needs to come out, the old unit is decommissioned or removed, the cylinder and loft tanks are taken out, and the pipework is re-run to the new boiler position. Expect it to cost more than a like-for-like combi swap — the survey prices it exactly.

Why bother

A back boiler typically runs at 70% efficiency or below against 90%+ for a modern condensing boiler — on the same gas bill, roughly a fifth of your spend is going up the flue. Parts are also increasingly scarce, so the next failure may force the decision anyway.