How Much Does Boiler Replacement Cost in the UK? 2026 Price Guide

The reason quotes land anywhere between £1,900 and £5,400 for what looks like the same job is that it isn't the same job. Three installers price three different scopes of work, and the homeowner assumes two of them are trying it on.

So before the price bands, work out what you're actually buying. Five minutes with a torch in the airing cupboard tells you more about your final bill than any online calculator.

Open the airing cupboard and look in the loft. What you find there decides which of four price brackets you sit in. Run through these in order and stop at the first one that describes your home.

• •Is the boiler under 10 years old with an intermittent fault? Get a diagnosis first. A diverter valve is £180-£320 fitted, a PCB £250-£450, an expansion vessel £160-£280. Replacing a 2019 boiler that keeps losing pressure is expensive when the answer is bleeding the radiators and re-pressurising or a £45 vessel recharge.
• •One boiler on the wall, no tanks anywhere, hot water on demand? That is a combi, and you need a straight swap. Cheapest bracket.
• •Boiler on the wall plus a hot water cylinder in the airing cupboard, but no tanks in the loft? That is a system boiler. Swapping like-for-like is mid-bracket; the cylinder may or may not need doing too.
• •Cylinder in the cupboard AND small tanks in the loft? That is a regular (heat-only) boiler. Converting to a combi is the priciest route: pipework, cylinder removal and making good.
• •Two bathrooms in use at once, or weak mains? Do not convert to a combi. Time a 2-litre jug at the kitchen tap: under 10 seconds is fine, over 15 seconds and a combi will disappoint you every morning.

These are fully fitted prices including VAT, a magnetic filter, commissioning and Building Regulations notification. Gas boiler work is standard-rated at 20% VAT, worth knowing when you compare it against what a heat pump costs — heat pump installation carries 0% VAT and qualifies for the Boiler Upgrade Scheme grant.

• •Combi to combi, same position, budget brand: £1,750-£2,300
• •Combi to combi, same position, premium brand with 10-12 year warranty: £2,300-£3,100
• •Combi moved to a different room: add £450-£900
• •System boiler swap, cylinder retained: £2,200-£3,000
• •System boiler plus new unvented cylinder: £4,200-£6,000
• •Regular boiler converted to combi (tanks and cylinder removed): £3,000-£4,800
• •Back boiler removal and full combi install: £3,400-£5,400
• •Oil boiler replacement, non-condensing to condensing: £3,200-£5,000

On a straight swap, materials are 65-75% of the bill and labour 25-35%. On a conversion that flips — labour and system work reach 55%, because the boiler is the easy part and the pipework isn't.

Merchant prices for the appliance are public, so there is no mystery to the boiler line. Installers add 10-20% on trade price, which is fair — that margin funds warranty registration and the return visit.

• •Combi boiler, 24-30kW: £750-£950 budget (Ideal Logic Max, Baxi 800), £1,050-£1,350 mid (Worcester Greenstar 4000, Vaillant ecoTEC plus), £1,350-£1,800 premium (Viessmann Vitodens 200-W, Worcester 8000 Life)
• •Horizontal flue kit and fittings: £110-£180. Vertical flue: £200-£380
• •Magnetic system filter fitted (Adey MagnaClean, Fernox TF1): £140-£190 — usually mandatory for warranty
• •Full power flush, 8-12 radiators: £420-£700. Chemical flush only: £130-£220
• •Gas supply upgrade to 22mm from the meter: £180-£420
• •Unvented cylinder, 180-250 litres, supplied and G3-certified: £1,900-£2,600
• •Smart control fitted: £180-£320 — see our pick of the best smart thermostats
• •Gas Safe engineer labour: £190-£280 a day outside the South East, £320-£480 in London, broadly tracking plumbers' hourly rates
• •Building Regulations notification: £55-£70, usually included

London and the South East run 20-30% above the Midlands, the North and Wales for identical work. Beyond region, what genuinely adds cost is access and system condition, not the appliance.

• •Moving the boiler: new flue penetration, gas run and condensate route, often scaffolding at £180-£400
• •Sludge. Black water from a radiator bleed valve means a power flush, and refusing one voids most warranties
• •Microbore pipework (8mm or 10mm) in 1970s and 80s houses, which restricts flow and often needs partial rerouting
• •Asbestos in a back boiler surround or old flue seal: £250-£600 for licensed removal
• •Warranty length. A 12-year warranty needs an accredited installer and adds £150-£300 up front
• •Timing. October and November quotes run 10-15% above the same job in May

Real job shapes, priced as a homeowner would receive them, VAT included.

• •Leeds, two-bed terrace, 2003 combi in the kitchen, like-for-like swap. Vaillant ecoTEC plus 825 £1,180; flue kit and fittings £145; magnetic filter £155; inhibitor, two new TRVs and sundries £110; labour one day £340; Building Regs £60. Total £1,990.
• •Bristol, three-bed semi, regular boiler with loft tanks and cylinder, converting to a combi. Worcester Greenstar 4000 30kW £1,320; cylinder removal and loft cleared £480; new 22mm gas run £290; pipework alterations and airing cupboard made good £420; 10-radiator power flush plus filter £620; labour two and a half days £860; Regs and sundries £180. Total £4,170.
• •South London, four-bed, two bathrooms, system boiler and failing cylinder. Viessmann Vitodens 100-W 26kW £1,420; 210-litre unvented cylinder £1,280; cylinder install and G3 certification £620; flue, filter and controls £540; labour three days at London rates £1,380. Total £5,240.

Get three quotes, and make one an online fixed-price installer as a benchmark that can't negotiate with itself. Then check the paperwork, not the total.

Sizing is where padding hides: a three-bed semi with ten radiators and one bathroom needs roughly 24-28kW, not the 35kW that gets quoted. If nobody counted your radiators or asked about bathrooms, they guessed. The same applies to blaming the boiler when one room is colder than the rest — that is usually balancing or a seized valve.

• •Check the engineer's Gas Safe number on the register's website, not on the van, and confirm the licence covers the appliance type
• •The quote must name the boiler model and kW output, the flue type, the filter, the flush method and who notifies Building Control
• •Ask for the Benchmark commissioning checklist to be completed and signed — without it, warranty claims get refused
• •Deposit no more than 25%. Pay the balance when the Building Regulations certificate lands, usually within 10 working days
• •Budget £90-£150 a year for the annual service. Skip it once and the 10-year warranty is gone

Figures come from installer quotes collected across Yorkshire, the South West and Greater London in early 2026, cross-checked against merchant list prices and three online fixed-price installers. Labour is priced in whole days, because that is how Gas Safe engineers quote replacements.

Apply a 0.85 multiplier for Northern Ireland, Wales and the North East, and 1.25 for inner London. Review the bands each autumn — appliance prices moved twice in 2025. And before committing to a new boiler, run the cheap wins: draught-proofing and a proper winter heating system check cost under £150 between them and occasionally show the boiler was never the problem.