Back Boiler Replacement Cost & Options 2026 (UK)
Replacing a back boiler costs £2,500–£4,500 in 2026 once you include removing the old unit from behind the fireplace and fitting a modern combi or system boiler in a new location. Back boilers — the units hidden behind a gas fire, like the Baxi Bermuda — are decades old, inefficient and no longer made, so replacement rather than repair is almost always the right call. Here are your options, the costs, and what to expect on the day.
2026 back boiler replacement costs
| Option | Typical price (2026) | Time |
|---|---|---|
| Remove back boiler + fit combi (relocated) | £2,500–£4,000 | 2–3 days |
| Remove back boiler + fit system boiler + cylinder | £3,200–£4,500 | 2–3 days |
| Removal & make-good of fireplace opening only | £400–£900 | 0.5–1 day |
| Builder's work / plastering after removal | +£200–£600 | +0.5–1 day |
| Power flush of old system | +£400–£700 | +0.5 day |
Your replacement options
Almost everyone replacing a back boiler moves to a wall-mounted combi in the kitchen, utility or airing cupboard — it removes the fire surround unit, frees up the chimney breast and gives instant hot water. If you have two or more bathrooms, a system boiler with an unvented cylinder is the better fit. The old gas fire is usually removed at the same time and the opening made good or fitted with a decorative surround.
Why back boilers are being retired
Back boilers date from the 1960s–1980s, run at around 55–65% efficiency against 90%+ for a modern condensing boiler, and are no longer manufactured, so spare parts are scarce. Keeping one going wastes money on gas and risks being left without heat when a part finally fails. Replacing it typically cuts heating bills noticeably and comes with a long manufacturer warranty.
What to expect on the day
Removing a back boiler is more involved than a standard swap because the unit sits behind the fireplace and the gas fire has to come out first. Expect two to three days: strip-out and make-good, then fitting the new boiler, pipework and flue in its new position, followed by a system flush and commissioning. A dust sheet and some redecoration around the old opening are normal.
FAQs
Related guides
- Combi boiler replacement
- System boiler installation
- What size boiler do I need?
- Is it worth it? Insights
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