The Short Answer
On our estimates, swapping a gas combi boiler for a new one in the same place costs about £2,000 to £3,200 fitted. Replacing a system or regular boiler and keeping the hot water cylinder is £2,500 to £4,000, and converting an older system to a combi, with the tanks and cylinder taken out, is £3,000 to £4,800.
A like-for-like swap takes about 6 to 8 hours; changing the type of boiler takes around 2 days. What moves the price most is whether the boiler stays where it is, and the make and warranty you choose.
New boiler cost calculator
A gas boiler supplied and fitted, by the job you need, plus the extras that change the price.
Estimated total
£2,000 to £3,200
| Combi for combi: boiler, fitting, controls and commissioning | £2,000 to £3,200 |
New boiler prices
| Job | Fitted cost |
|---|---|
| Combi for combi (same place, same type) | £2,000 to £3,200 |
| System or regular (keeping the hot water cylinder) | £2,500 to £4,000 |
| Convert to a combi (tanks and cylinder taken out) | £3,000 to £4,800 |
| Moving the boiler to another room | £400 to £1,200 |
| Flue through the roof, or a longer run | £150 to £500 |
| Magnetic system filter, if not included | £180 to £260 |
Combi, system or regular?
Worcester Bosch, the boiler maker, sums up the three types:
- Combi: heats water straight from the mains when you turn on a tap, so there's no hot water cylinder and no tank in the loft. It suits smaller homes.
- System: stores hot water in a cylinder but needs no loft tank. It's the better fit for homes with more than one bathroom, and it works with solar water heating.
- Regular (heat only): the traditional set-up with a cylinder and tanks, for homes that already have it.
I'd keep the type you have unless it isn't working for you: converting costs more because pipework changes and the cylinder and tanks come out. With more than one bathroom, Worcester's own advice points to a system boiler and a cylinder.
What the price should include
In England, Approved Document L sets what a replacement gas boiler has to meet, and a carbon monoxide alarm is now part of the job too. Check each quote covers:
- An efficient boiler: at least 92% efficient (ErP) in an existing home. A combi should be chosen to turn down to suit the home's heating load.
- Cleaning the system: the heating circuits cleaned and flushed before the new boiler goes on, an inhibitor added, and the system commissioned to BS 7593.
- Room controls: when a boiler is replaced, each room should have its own thermostatic control where that's feasible.
- A carbon monoxide alarm in the room with the boiler: Approved Document J asks for one with any new or replacement gas appliance other than a cooker.
- Registration: the engineer notifies the job through Gas Safe Register within 30 days, and a Building Regulations certificate arrives by post in 10 to 15 working days. Keep it: it belongs to the property, and Gas Safe Register says it's useful when you sell or remortgage.
Get the make, model and warranty length in writing on every quote, so you're comparing like for like. Ask whether a magnetic filter is included.
How long it takes
BOXT, a national installer, puts a like-for-like swap in the same place at about 6 to 8 hours, and a change of type (system to combi, say) at around 2 days, because floorboards come up and new pipes go in. The job runs: drain down, take the old boiler out, flush the system, fit the new boiler, then test, commission and show you the controls. You'll be without heating and hot water for that time, so I'd avoid booking it in a cold snap if you have the choice.
Free boilers and grants
The Energy Company Obligation (ECO) can pay to replace or repair a boiler if you get certain benefits (Universal Credit, Pension Credit, Child Benefit and Housing Benefit among them) and live in private housing. Owners need an energy performance rating of D to G; private tenants E to G, with the owner's permission. You apply through your council or an energy supplier. The current scheme, ECO4, runs until 31 December 2026. GOV.UK warns that installers may contact you directly, so check with the council or supplier if you're unsure.
There's no grant for a new gas boiler otherwise. In England and Wales the Boiler Upgrade Scheme takes £7,500 off an air or ground source heat pump, £5,000 off a biomass boiler and £2,500 off an air-to-air heat pump. Your MCS-certified installer applies for it. See the grant in full. If you're off the gas grid or curious, get a heat pump quote alongside.
VAT: HMRC treats a new boiler as standard-rated, so the full 20% applies, unlike heat pumps and insulation.
Checking the engineer
Fitting a gas boiler must be done by a Gas Safe registered engineer: it's the law. Ask to see their Gas Safe ID card. It carries their photo, business, registration number and start and expiry dates (the licence is renewed every year), and the back lists the kinds of gas work they're qualified for: not every engineer can work on every appliance, so check it says domestic boilers.
Repair or replace?
E.ON Next, the energy supplier, puts a boiler's life at around 10 to 15 years. I wouldn't replace one that's working and serviced on age alone. But once an older boiler needs a big part, such as a heat exchanger or circuit board, I'd put that money towards a new boiler instead. Prices for the common faults are on our boiler repair costs page; to keep the new one under warranty, see boiler servicing.
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Frequently asked questions
How much should a replacement boiler cost?
On our estimates, about £2,000 to £3,200 to swap a gas combi in the same place, £2,500 to £4,000 for a system or regular boiler, and £3,000 to £4,800 to convert to a combi.
Can I get a new boiler for free?
Possibly, through the Energy Company Obligation, if you get certain benefits, live in private housing and the home's energy rating is D to G (E to G if you rent privately). Apply through your council or an energy supplier. ECO4 runs until 31 December 2026.
Is it worth replacing a 15-year-old boiler?
Boilers last around 10 to 15 years, so a 15-year-old one is at the end of that. If it's working and serviced, there's no rule saying you must; if it needs an expensive part, I'd usually put the money towards a new one.
How long does it take to fit a new boiler?
About 6 to 8 hours for a like-for-like swap in the same place, and around 2 days when you change the type of boiler, BOXT says.
Is there VAT on a new boiler?
Yes, at the standard rate. HMRC's zero rate for energy-saving installations covers heat pumps, solar and insulation, not boilers.
Do I need a carbon monoxide alarm with a new boiler?
In England, yes: building regulations ask for a carbon monoxide alarm in the room when a new or replacement gas appliance, other than a cooker, is fitted.
How we priced thisView sources (14, 9 official)
Rules come from the legislation and official guidance, read at source. Prices are our estimates: we check them against trade price data, retailer shelf prices and specialists' price lists, then build them up from their parts so the totals add up. Below are the sources behind the page; the trade price guides we only compare against aren’t listed. Where sources disagreed, we've said so. More on our method.
- OfficialApproved Document L: Conservation of fuel and power, Volume 1 Dwellings (2021 edition incorporating 2023 amendments), GOV.UK. Checked 16 Oct 2026.
- OfficialApproved Document J: Combustion appliances and fuel storage systems (2010 edition incorporating 2010, 2013 and 2022 amendments), GOV.UK. Checked 16 Oct 2026.
- OfficialThe Gas Safety (Installation and Use) Regulations 1998, regulation 3, legislation.gov.uk. Checked 15 Oct 2026.
- OfficialUnderstand the Gas Safe ID card, Gas Safe Register. Checked 15 Oct 2026.
- OfficialBuilding Regulations Certificate, Gas Safe Register. Checked 15 Oct 2026.
- OfficialHelp from your energy supplier: the Energy Company Obligation, GOV.UK. Checked 16 Oct 2026.
- OfficialExtending the ECO4 end date (consultation outcome, updated 23 January 2026), GOV.UK. Checked 16 Oct 2026.
- OfficialApply for the Boiler Upgrade Scheme: what you can get, GOV.UK. Checked 15 Oct 2026.
- OfficialEnergy-saving materials and heating equipment (VAT Notice 708/6), HM Revenue & Customs. Checked 16 Oct 2026.
- IndustryBoilers explained, Worcester Bosch. Checked 15 Oct 2026.
- IndustryBoilers (fixed installed prices), BOXT. Checked 16 Oct 2026.
- IndustryHow long does it take to fit a new boiler?, BOXT. Checked 16 Oct 2026.
- IndustryHow much does a new boiler cost?, E.ON Next. Checked 16 Oct 2026.
- IndustryNew boilers, British Gas. Checked 15 Oct 2026.
