Back boiler replacement
Back boiler replacement starts with a boiler that sits behind a gas fire in the fireplace. Replacing one means a boiler in a new place, a new flue and usually new pipework, so it costs more than a like-for-like swap and takes longer.
Who back boiler replacement suits
Suits
- Homes with an old back boiler behind a fire
- Anyone who wants the fireplace back
- Owners moving to a modern condensing boiler
Good points
- Replaces a very old, inefficient boiler
- Frees the fireplace
- Moves to a modern condensing boiler with a warranty
Watch out for
- The dearest kind of boiler swap
- Needs a new boiler position and flue route
- Longer job with more disruption
What back boiler replacement costs
Back boiler replacement typically costs £4,400 (Back boiler to gas combi, fitted), with most jobs between £3,000 and £6,000. That includes VAT at 20%. Fitting takes 2–4 days on site.
What you would actually pay
Typical Back boiler to gas combi, fitted · UK- Typical installed cost Back boiler replacement, supplied and fitted
- £3,667
- VAT at 20% Standard rate
- £733
- Net cost to you
- £4,400
If you borrowed £4,400.00 over 36 months at 0.0%, it would cost £122.22 a month – £4,400.00 in total, of which £0.00 is interest. The last payment would be £122.30.
Illustration only – not a quote, not an offer of credit, and not financial advice. Rates depend on your circumstances and creditworthiness.
Where the money goes on back boiler replacement
| Element | Typical range |
|---|---|
| Back boiler to gas combi A new gas combi boiler fitted in a new position, with a new flue and the pipework changed. This row is the headline price and covers the range. | £3,000 – £6,000 |
| Gas pipe or flue upgrade A longer gas run, flue extension or new flue terminal where the old route will not do. | £140 – £500 |
| Power flush Cleaning the radiators and pipework before the new boiler goes on. Optional, and worth asking about on an old system. | £350 – £1,000 |
Guide prices including VAT. Your actual cost depends on your home, access and specification.
What moves the price of back boiler replacement
- How much changes
A like-for-like swap is the cheapest job. Changing type, moving the boiler or re-routing the flue adds pipework, labour and days.
- Where you live
Engineers charge more in London and the South East than in the North and in Scotland, and the regional pages show the difference.
- The boiler itself
Budget ranges cost the least and premium ranges with longer warranties cost the most.
- The state of the system
Old pipes and radiators full of sludge can need a power flush or new valves before an installer will fit a new boiler under warranty.
What a quote for back boiler replacement should include
If a quote is missing any of these, ask why before you compare it with another.
- The make, model and output of the new boiler, and the length of the manufacturer warranty
- What the job includes: removing the old boiler, new pipework, the flue, the condensate pipe and making good
- Whether a magnetic filter and a system clean or flush are included, and what it costs if the system needs one
- Whether the engineer is Gas Safe registered, and who registers the installation with the manufacturer
- The days the heating and hot water will be off, and the deposit and payment schedule
- Whether the price includes VAT
- Who makes good the fireplace and the hole in the chimney breast after the old boiler comes out
Back boiler replacement prices by region
Labour is most of the difference. Typical price (Back boiler to gas combi, fitted), including VAT.
| Region | Typical | vs UK average |
|---|---|---|
| London | £5,500 | +25% |
| South East | £5,200 | +17% |
| South West | £4,800 | +10% |
| East of England | £4,700 | +6% |
| West Midlands | £4,600 | +4% |
| Scotland | £4,500 | +2% |
| East Midlands | £4,400 | UK average |
| Yorkshire and the Humber | £4,400 | UK average |
| North West | £4,300 | −2% |
| North East | £4,200 | −5% |
| Wales | £4,100 | −6% |
| Northern Ireland | £3,900 | −12% |
Common questions about back boiler replacement
Why does replacing a back boiler cost more?
The new boiler goes somewhere else, so the installer needs a new flue, new pipework and some making good where the old boiler sat.
Do I have to move the boiler?
Usually yes. A modern boiler does not fit behind a fire in the way the old back boiler did, so the installer chooses a new position, often a kitchen wall or the loft.
How long does it take?
It varies with the layout, but expect a few days and the heating off for part of that.
Does the engineer have to be Gas Safe registered?
Yes. Work on a gas boiler has to be done by a Gas Safe registered engineer, and you should check their ID card before they start. Our Gas Safe Register guide shows how.
Is VAT included in the price shown?
Yes. Every price on this site includes VAT. A VAT-registered business normally charges it on boiler work, and an engineer who is not registered does not, so put quotes on the same basis before you compare them.
Where these back boiler replacement prices come from
Guide prices are compiled from published UK price guides, converted to a price before VAT, and shown here with VAT added. They are indicative, not quotations. How we price explains the method.
Get quotes for your home
A guide price only takes you so far. Local firms can price the work on your own home, and comparing a few quotes is the quickest way to see what is reasonable.
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