Gas combi boilers
A gas combi boiler heats the radiators and makes hot water on demand from the mains, so there is no hot water cylinder and no header tank in the loft. It is the standard choice in UK homes with one or two bathrooms, and the cheapest type to fit in place of an old boiler.
Who gas combi boilers suit
Suits
- Flats and houses with one or two bathrooms
- Homes where space is tight and a cylinder would not fit
- Anyone replacing an existing combi in the same place
Good points
- The cheapest boiler type to fit
- Hot water on demand, with no cylinder to heat or store
- Compact enough for a kitchen cupboard or the loft
- Fewer parts, so a quicker installation
Watch out for
- Hot water comes from the mains, so low mains pressure shows
- One hot tap at full flow is fine, two at once can be a squeeze
- No stored hot water if the boiler breaks down
What gas combi boilers cost
Gas combi boilers typically cost £2,700 (24 to 30kW gas combi boiler, like-for-like swap, fitted), with most jobs between £1,800 and £3,500. That includes VAT at 20%. Fitting takes 1–2 days on site.
What you would actually pay
Typical 24 to 30kW gas combi boiler, like-for-like swap, fitted · UK- Typical installed cost Gas combi boilers, supplied and fitted
- £2,250
- VAT at 20% Standard rate
- £450
- Net cost to you
- £2,700
If you borrowed £2,700.00 over 36 months at 0.0%, it would cost £75.00 a month – £2,700.00 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 gas combi boilers
| Element | Typical range |
|---|---|
| Boiler and fitting, like for like A new gas combi boiler of the right output, fitted in place of the old one, with a standard flue. This row is the headline price and covers the range for the output and make you choose. | £1,800 – £3,500 |
| 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. | £400 – £700 |
| Magnetic filter Catches the iron sludge that wears out a boiler, and many manufacturers ask for one under their warranty terms. | £120 – £200 |
| Smart thermostat A programmable or smart thermostat in place of the old wall control. Optional, and sometimes offered free by the installer. | £140 – £300 |
Guide prices including VAT. Your actual cost depends on your home, access and specification.
What moves the price of gas combi boilers
- The boiler itself
Budget ranges cost the least, mid-range ranges sit in the middle, and premium ranges with longer warranties cost the most. Output matters less to the price than the range does.
- Like for like or a conversion
Swapping a boiler for the same type in the same place is the cheapest job. Changing type, moving the boiler or re-routing the flue adds pipework, labour and days.
- The state of the system
Old radiators and pipes full of sludge can need a power flush, new valves or a filter before the installer will fit a new boiler under warranty.
- Where you live
Installer rates are higher in London and the South East than in the North and in Scotland, and the regional pages show the difference.
- Who fits it
National installers and local Gas Safe engineers quote differently for the same boiler. Compare quotes on the make and model, the warranty and what is included, not on the headline price alone.
What a quote for gas combi boilers 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 boiler, and the length of the manufacturer warranty once it is registered
- Whether the price includes a magnetic filter, a system clean or flush, and the cost if the installer finds the system needs one
- Whether the flue, the condensate pipe and any new pipework are included, and what a longer or relocated flue adds
- Removal and disposal of the old boiler, and who registers the installation with Gas Safe and the manufacturer
- A fixed price in writing, the deposit and the payment schedule, and the workmanship guarantee
- The date, the number of engineers and how many days the heating and hot water will be off
Gas combi boilers prices by region
Labour is most of the difference. Typical price (24 to 30kW gas combi boiler, like-for-like swap, fitted), including VAT.
| Region | Typical | vs UK average |
|---|---|---|
| London | £3,400 | +25% |
| South East | £3,200 | +17% |
| South West | £3,000 | +10% |
| East of England | £2,900 | +6% |
| West Midlands | £2,900 | +4% |
| Scotland | £2,800 | +2% |
| East Midlands | £2,700 | UK average |
| Yorkshire and the Humber | £2,700 | UK average |
| North West | £2,700 | −2% |
| North East | £2,600 | −5% |
| Wales | £2,600 | −6% |
| Northern Ireland | £2,400 | −12% |
Common questions about gas combi boilers
What size combi boiler do I need?
It depends on the number of bathrooms and radiators, not only on the size of the house. A smaller output suits a flat or a house with one bathroom, a middle output suits a typical three-bedroom house, and a larger output suits a house with two or more bathrooms. Your installer should size it with a heat loss check.
How long does it take to fit a combi boiler?
A like-for-like swap usually takes between four and six hours. Moving the boiler or converting from a system or regular boiler takes longer, often two to three days.
Can a combi boiler run a house with two bathrooms?
A larger-output combi can serve two bathrooms if the mains pressure and flow are good, but two showers at once will slow each other down. A system boiler with a cylinder copes better in a busy household.
Is VAT charged on a new gas boiler?
Yes. Gas boilers are standard-rated, so the price shown includes VAT. The zero rate for energy-saving materials applies to heat pumps, solar panels and insulation, not to gas boilers.
Where these gas combi boilers 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.
- BestBuilders, combi boiler cost guide, dated 22 August 2026 (VAT treatment not stated; treated as including VAT and divided by 1.2 to store ex-VAT)
- MyJobQuote, new central heating and combi boiler cost, updated 20 October 2026 (VAT treatment not stated; treated as including VAT and divided by 1.2)
- greatbritishenergy.com, new boiler cost guide, updated 30 October 2026, quoting Checkatrade fitted prices and Which? brand prices (gas boilers standard-rated at 20%; the page does not say whether its figures include VAT, so they are treated as including it and divided by 1.2)
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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