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A new boiler in London costs £1,800 to £4,500 fitted: a combi swapped like for like is £2,200 to £3,500, a system or conventional boiler replaced in place £2,600 to £4,000, and a conversion to a combi with the tanks removed £3,500 to £5,000. London labour runs 20 to 30 per cent above the UK, and a period house often adds flue or gas-pipe work.
| Job | London low | London typical | London high | UK typical | What moves the price |
|---|---|---|---|---|---|
| Combi swap, like for like | £1,800 | £2,500 | £3,500 | £2,300 | Fixed-price packages from £1,979 to £2,499; 24 to 28kW suits a 1 or 2 bed flat |
| Combi swap with pipework or flue changes | £3,000 | £3,500 | £4,500 | £3,000 | Victorian and Edwardian homes: gas pipe upsizing, flue rerouting |
| System boiler, replaced in place | £2,600 | £3,200 | £4,000 | £2,600 | Keeps the hot water cylinder |
| Conventional (heat-only) boiler, like for like | £2,200 | £3,000 | £3,800 | £2,600 | Keeps the tanks in the loft |
| Conversion to a combi, tanks and cylinder removed | £3,500 | £4,200 | £5,000 | £2,800 | Frees the airing cupboard and loft; needs good mains pressure |
| System boiler plus unvented cylinder (3+ bed, 2+ bathrooms) | £4,200 | £5,000 | £6,000 | The London answer for two showers running at once | |
| Add-on: moving the boiler to another room | £300 | £750 | £2,000 | £750 | Flue extension £75 to £125 a metre |
A boiler replacement is a one-day job for a like-for-like swap and two to three for a conversion: the old unit out, the new one on the wall with a new flue, a magnetic filter on the return, the system flushed and inhibited, and the boiler commissioned with the Benchmark checklist that keeps the warranty valid. Since 2018 every new gas boiler in England must be at least 92 per cent efficient and fitted with time and temperature controls, and a combi needs weather or load compensation or a smart control as well.
The engineer must be on the Gas Safe Register; check the seven-digit number on their card by texting Gas and the number to 85080 before they start. They notify the installation to building control within 30 days and the compliance certificate arrives by post, which you will need when you sell.
London changes three things. Labour is 20 to 30 per cent above the UK, and firms price in ULEZ, the Congestion Charge and permit parking in boroughs like Camden and Westminster. Mansion-block flats can need scaffolding or rope access for the flue. And a quarter of inner-London homes have no mains gas, where an electric boiler at £1,500 to £3,300 is the answer.
Prices last checked: September 2026. Based on the published 2026 prices of three London heating firms, Heatable's national fixed prices and its median quote for January to May 2026, and MyJobQuote's 2026 guide. PROS AI does not yet have enough completed boiler installations in London to publish its own averages.
£2,200 to £3,500 for a like-for-like swap from most London firms, with fixed-price packages from £1,979 to £2,499 that include the boiler, flue and magnetic filter. Nationally the median quote in 2026 is about £2,300. Pipework, a new flue route or a premium brand take it to £3,000 to £4,500.
£3,500 to £5,000 in London: the boiler, the removal of the cold water tank and hot water cylinder, new pipework and usually a day or two more labour than a swap. It only makes sense if your mains pressure is good; a large house with two bathrooms is often better served by a system boiler with an unvented cylinder at £4,200 to £6,000.
Yes, but the engineer handles it. A Gas Safe registered engineer notifies the installation through the Gas Safe Register within 30 days and you receive a Building Regulations compliance certificate by post in 10 to 15 working days. Keep it with the house documents; solicitors ask for it on a sale or remortgage.
Mid-tier boilers from Ideal and Baxi start around £1,300 to £2,500 fitted nationally and carry 5 to 7 year warranties; Worcester Bosch, Vaillant and Viessmann run £1,500 to £3,700 with 7 to 10 years on the premium ranges. In London the unit alone starts at about £1,500 for Ideal and £1,800 to £2,000 for the premium three. The warranty only holds if the boiler is serviced every 12 months.
A 24 to 28kW combi covers a one or two bed flat with one bathroom; a three or four bed house needs 30 to 32kW. Bigger is not better: an oversized combi cycles on and off and costs more to run. The engineer sizes it from the number of radiators, bathrooms and the mains flow rate.
Written by Shay Hazan, PROS AI.
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