Anyone who works on a gas boiler in London must be on the Gas Safe Register, and you can check an engineer's number before they start. Installations, repairs, annual services, power flushes and landlord gas safety certificates are priced very differently, so the pages below give a London range for each one and explain what changes it. For a suspected gas leak call the National Gas emergency line on 0800 111 999 first.
Also on PROS AI: Electricians in London and Plumbers in London.
A heating engineer in London charges £60 to £125 for a weekday call-out and £80 to £140 an hour, £140 to £260 for the first hour out of hours. Fixed-price jobs run from £80 to £150 for a boiler service and £150 to £400 for most repairs to £1,800 to £3,500 for a like-for-like combi swap.
| Job | London low | London typical | London high | UK typical | What moves the price |
|---|---|---|---|---|---|
| Annual boiler service | £80 | £95 | £150 | £100 | Book in September or early October; November to January is the rush; the warranty only holds if the boiler is serviced every 12 months |
| Landlord gas safety certificate (CP12) | £50 | £80 | £120 | £75 | Boiler and one appliance; £10 to £20 per extra appliance; £85 to £180 combined with a service in one visit |
| Call-out and diagnosis, weekday | £60 | £120 | £125 | £80 | Often waived if you go ahead with the repair; out of hours £140 to £260 for the first hour, then £110 to £160 |
| Boiler repair, pressure loss, expansion vessel or valve | £120 | £200 | £280 | The typical winter fault; a fan is £200 to £420, a diverter valve £150 to £390, a circuit board £290 to £650 | |
| Combi boiler, like-for-like swap | £1,800 | £2,500 | £3,500 | £2,300 | Fixed-price packages from £1,979 to £2,499; pipework or flue changes take it to £3,000 to £4,500 |
| System boiler, replaced in place | £2,600 | £3,200 | £4,000 | £2,600 | Keeps the hot water cylinder; a conversion from a conventional boiler to a combi is £3,500 to £5,000 |
| Power flush, 8 radiators | £580 | £680 | £800 | £495 | £60 to £85 per radiator; 6 radiators £450 to £620, 10 radiators £700 to £950; Zones 1 and 2 add 10 to 15 per cent |
| Radiator replacement, like-for-like panel radiator, supplied and fitted | £180 | £250 | £320 | £200 | 1 to 2 hours; a towel rail £250 to £420, a vertical designer radiator £450 to £850; a single valve replaced is £100 to £200 |
| Smart thermostat, supplied and fitted | £160 | £280 | £400 | £265 | Labour only £80 to £150 if you supply the unit; the unit is £100 to £220 by brand; 1 to 2 hours |
| Unvented hot water cylinder, like-for-like, fully fitted | £1,495 | £2,095 | £2,845 | 150 to 300 litres; includes the G3 notification, commissioning and disposal; a vented to unvented conversion starts at about £2,495 |
Heating and boiler engineers in London look after the gas boiler and everything it feeds: annual services and landlord gas safety certificates, breakdowns and repairs, like-for-like boiler swaps and conversions, hot water cylinders, power flushes, radiators, valves and thermostats. A service, a certificate or a common repair is a fixed price plus parts; a new boiler is quoted after a survey of the flue, the gas pipe and the water pressure, and a good quote itemises the boiler, the filter, the flush and the controls.
For anything on the gas side the law is simple: the engineer must be on the Gas Safe Register, and it is illegal for anyone else to fit, service or repair a gas boiler. Ask for the ID card and look at both sides: the front carries the photo, the seven-digit licence number and an expiry date, and the back lists the types of gas work the engineer is qualified for, so a boiler engineer's card should say boilers, not just cookers. Confirm the number online through the register's Check an Engineer search, by texting Gas and the number to 85080, or on 0800 408 5500. A new boiler is also notifiable under the Building Regulations; the engineer registers it through the Gas Safe Register within 30 days and the compliance certificate arrives by post. Unvented cylinders need an engineer with the G3 qualification. Radiators, valves and the wet side of the system are plumbing, so a plumber without gas registration can do them.
A weekday call-out of £60 to £125 covers the visit and the diagnosis, and many London firms waive it if you go ahead with the repair; labour is then £80 to £140 an hour with the part on top. Out of hours the first hour is £140 to £260, so a boiler that is losing pressure but still running is cheaper to book for the morning. For a new boiler, get two or three written quotes that name the boiler model, the warranty length, the magnetic filter and the flush, and check whether the price includes VAT and removal of the old unit.
London prices run 20 to 30 per cent above the UK: a service is £80 to £150 against about £100, an hour of labour £80 to £140 against £70, and a like-for-like combi swap typically £2,500 against £2,300. Firms price in the Congestion Charge, ULEZ and permit parking, mansion-block flats can need scaffolding for the flue, and London's hard water makes a magnetic filter and regular flushing standard rather than optional. Book a service in September or early October; November to January is the breakdown rush.
For the job you have in mind, read the guides on new boiler installation and replacement, boiler repairs and servicing, emergency boiler breakdowns, central heating diagnostics and repairs, power flushing and general heating work, each with its own London price table, and the plumbing guide on hot water cylinders and water tanks.
Prices last checked: September 2026. Based on the London and UK figures already published on the individual heating job pages, which draw on the 2026 price pages of London heating firms and UK cost guides, plus 2026 radiator and smart thermostat guides with London figures for the two rows without a job page; where a source published only a range, the typical column shows the middle of that range. PROS AI does not yet have enough completed heating jobs in London to publish its own averages.
£80 to £140 an hour on a weekday, against about £70 across the UK, with a call-out and diagnosis fee of £60 to £125 that many firms waive if you go ahead with the repair. Out of hours the first hour is £140 to £260 and each hour after £110 to £160. Common repairs are done within one to two hours, so £150 to £400 including the part is the usual bill.
£80 to £150, typically about £95, against about £100 across the UK. A landlord gas safety certificate is £50 to £120 for the boiler and one appliance, and £85 to £180 buys both in one visit, which is cheaper than two. Book in September or early October; from November to January engineers are on breakdowns and waiting times stretch. An annual service keeps the warranty valid.
Ask to see the engineer's ID card, then check the seven-digit licence number online through the Gas Safe Register's Check an Engineer search, by texting Gas and the number to 85080, or on the free helpline 0800 408 5500. The front of the card shows the photo and the expiry date; the back lists the types of gas work the engineer is qualified for, and boilers should be on it.
£1,800 to £4,500 fitted for most homes: a combi swapped like for like is £1,800 to £3,500 and typically £2,500, a system or conventional boiler replaced in place £2,200 to £4,000, and a conversion from a conventional boiler to a combi with the tanks removed £3,500 to £5,000. A system boiler with a new unvented cylinder for a house with two bathrooms is £4,200 to £6,000.
£450 to £800 for most homes: £450 to £620 for six radiators, £580 to £800 for eight and £700 to £950 for ten, which is £60 to £85 a radiator against about £495 for eight radiators across the UK. Central London quotes run 10 to 15 per cent higher and a quote well under £50 a radiator usually means corners cut. A magnetic filter fitted at the same time adds £150 to £240.
Written by PROS AI editorial team.
