Boiler conversions
A boiler conversion replaces a system or regular boiler with a gas combi, which usually means taking out the hot water cylinder and the loft tanks and re-plumbing the system. It frees the space and gives hot water on demand, and it costs more than a like-for-like swap because of the extra pipework and days.
Who boiler conversions suit
Suits
- Smaller homes that want the cylinder and loft tanks out
- Anyone replacing a regular or system boiler and wanting a combi
- Homes with one or two bathrooms
Good points
- Frees the cupboard and the loft space
- Hot water on demand
- Often a lower running cost for a small household
Watch out for
- Costs more than swapping a combi for a combi
- Low mains pressure can make a combi a poor fit
- Takes two to three days
What boiler conversions cost
Boiler conversions typically cost £3,600 (System or regular boiler to gas combi, fitted), with most jobs between £2,800 and £4,500. That includes VAT at 20%. Fitting takes 2–3 days on site.
What you would actually pay
Typical System or regular boiler to gas combi, fitted · UK- Typical installed cost Boiler conversions, supplied and fitted
- £3,000
- VAT at 20% Standard rate
- £600
- Net cost to you
- £3,600
If you borrowed £3,600.00 over 36 months at 0.0%, it would cost £100.00 a month – £3,600.00 in total, of which £0.00 is interest.
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 boiler conversions
| Element | Typical range |
|---|---|
| System or regular boiler to gas combi A new gas combi boiler fitted in place of a system or regular boiler, with the cylinder and tanks removed and the pipework changed. This row is the headline price and covers the range. | £2,800 – £4,500 |
| Moving the boiler New pipework and a new flue route when the boiler goes somewhere else in the house. Optional, and the labour grows with the distance. | £400 – £1,000 |
| 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 boiler conversions
- 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 boiler conversions 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
- What happens to the old cylinder and tanks, and whether disposal is included
Boiler conversions prices by region
Labour is most of the difference. Typical price (System or regular boiler to gas combi, fitted), including VAT.
| Region | Typical | vs UK average |
|---|---|---|
| London | £4,500 | +25% |
| South East | £4,200 | +17% |
| South West | £4,000 | +10% |
| East of England | £3,800 | +6% |
| West Midlands | £3,700 | +4% |
| Scotland | £3,700 | +2% |
| East Midlands | £3,600 | UK average |
| Yorkshire and the Humber | £3,600 | UK average |
| North West | £3,500 | −2% |
| North East | £3,400 | −5% |
| Wales | £3,400 | −6% |
| Northern Ireland | £3,200 | −12% |
Common questions about boiler conversions
Can I convert to a combi if I have a big family?
A combi supplies hot water on demand, so two bathrooms running at once will slow each other down. Households with high hot water use are often better with a system boiler and a cylinder.
How long does a conversion take?
A system or regular boiler to a combi takes longer than a like-for-like swap, often two to three days, because of the pipework.
Will I need to heat a cylinder again later?
Possibly. Most heat pumps work with a hot water cylinder, so a home that moves to a combi now may need one back if it fits a heat pump in future.
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 boiler conversions 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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