Back boilers
Back boiler replacement
Got an old back boiler behind a gas fire? Most are 40–50 years old, around 55–65% efficient, and parts are almost impossible to find. We remove the fire and back boiler, fit a modern Worcester or Viessmann combi and make the fireplace good — usually in two days, at a fixed price.
Back boiler replacement cost (2026)
Back boiler to combi
Most common — removes tanks and cylinder too
from £3,100 inc VAT
Back boiler to system boiler
Keeps a hot water cylinder, ideal for 2+ bathrooms
from £3,450 inc VAT
Back boiler to regular boiler
Like-for-like, keeps loft tanks
from £2,950 inc VAT
Replacement gas or electric fire
Optional, fitted in the same visit
quoted on survey
All prices include VAT. Includes standard flue, fitting and system flush. Confirmed after a free survey.
Signs it's time to replace your back boiler
Pilot light keeps going out
The most common back boiler fault — thermocouples and gas valves are wearing out and often obsolete.
Engineer can't get parts
Baxi Bermuda and Glow-worm back boiler parts are discontinued. A repair can take weeks, if it's possible at all.
High gas bills
At 55–65% efficiency, up to £400 a year of gas is going up the chimney compared with a modern A-rated boiler.
Failed safety check
Spillage or flue test failures mean the appliance may be capped off as 'At Risk' — replacement is usually the only real fix.
What the job involves
- Gas fire and back boiler removed and disposed of
- Chimney or flue swept, lined or capped as required
- New combi fitted in the kitchen, utility or airing cupboard
- Loft tanks and hot water cylinder removed on combi conversions — frees up a cupboard
- Full system powerflush using our own machine — old systems are always sludged
- Magnetic filter fitted to protect the new boiler warranty
- Fireplace opening made good and left clean
- Gas Safe and Building Control notified, warranty registered for you
How much could you save?
A typical semi in Birmingham with a 1970s back boiler uses around 15,000 kWh of gas a year. A new Worcester Greenstar or Viessmann Vitodens at 92%+ efficiency cuts that by roughly a third — around £300–£400 a year at current prices.
Over the 10–12 year guarantee on a new boiler, that's £3,000–£4,800 saved — enough to cover most of the install on its own.
Free quote
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60 second boiler quote
No callbacks unless you want one
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Back boiler FAQs
How much does it cost to replace a back boiler?
Back boiler to combi conversions start from £3,100 inc VAT, including removal of the fire, back boiler, tanks and cylinder, a powerflush, filter and making good. Your free survey gives you a fixed written price.
How long does a back boiler replacement take?
Usually two days. Day one removes the old system and runs new pipework; day two fits and commissions the new boiler and makes good.
Are back boilers still legal?
Yes, an existing back boiler can stay if it passes its safety checks. But new ones can't be fitted, parts are scarce, and any failed spillage test means it can be capped off.
Where will the new boiler go?
Most customers choose the kitchen, utility or the airing cupboard freed up by removing the cylinder. We'll talk through the options on survey.
What happens to my fireplace?
We make the opening good, cap or line the chimney as required, and can fit a replacement gas or electric fire in the same visit if you want one.
Can I keep my radiators?
Usually yes. We powerflush the system first and only recommend replacing radiators that are leaking or badly corroded.