Repair or replace your boiler? An honest way to decide

Start with safety, then with the quote

If you smell gas, leave the house, do not use light switches or anything with a flame, open doors and windows on the way out if it is safe, turn the gas off at the meter if you can reach it safely, and call the National Gas Emergency Service on 0800 111 999 (0800 002 001 in Northern Ireland). If a carbon monoxide alarm sounds, get everyone out, make the same call and get medical help if anyone feels unwell. Our gas leak guide has the full steps. Whatever you decide about the boiler, make sure a working carbon monoxide alarm is fitted near it.

If an engineer has left a 'Danger Do Not Use' label, that is an instruction to stop using the appliance, not a verdict to buy a new one. The Gas Safe Register explains that the label covers two findings: Immediately Dangerous, 'an immediate danger to life and property if left operating', and At Risk, where a fault 'could constitute a danger to life or property without further faults developing'. In both cases the engineer asks your permission to turn it off or disconnect it, and it stays off until repaired. The HSE adds that it is illegal to use a gas appliance you suspect is unsafe.

The useful next step is paper. The Gas Safe Register says the engineer should give you a gas warning notice with precise details of the fault. Keep it, pass a copy to your landlord if you rent, and ask three things: what would make the boiler safe, whether the part is available, and what that costs against a replacement. Being told an installation 'doesn't comply with current standards' is different: the Gas Safe Register says acting on that 'is completely up to you'. Never remove the label, and never open the casing or touch the gas valve, flue or burner: by law, that is a Gas Safe registered engineer's work.

If the boiler is unreliable rather than condemned, the resident's part is short, and we cover it in boiler stopped working in the cold: power, settings and timer, the pressure gauge and filling loop as your manual describes, one reset as the manual shows, and thawing an outside condensate pipe with warm, never boiling, water. Everything else is a Gas Safe engineer's job, and the quote they hand you is where this guide begins.

The questions that move the answer

How old is it? The sources we read put a serviced boiler's life at about 10 to 15 years. The Energy Saving Trust says 'the average lifespan of a boiler is 10 to 15 years'; Worcester Bosch and Baxi say 10 to 15 with servicing, Vaillant typically 15 and Viessmann up to 15 or longer. Makers sell replacements, and none gives a hard stop. Which? pulls the other way: because heating systems are so expensive to install, it does not recommend replacing a boiler before it is necessary. Age is a prompt to ask harder questions, not a reason on its own.

For a sense of how an official body weighs age against repair cost, Ofgem's ECO4 rules treat a mains-gas combi as beyond economic repair if the repair would cost more than about £3,490 at one year old, falling by roughly £290 a year to about £870 at ten, about £290 at twelve and nothing from thirteen (ex VAT, from its 2022 heating checklist, so dated). Ofgem says the ceilings reflect replacement cost and depreciation. That is an eligibility rule for a means-tested scheme, not advice for a household paying its own bill, but it shows the shape: the older the boiler, the smaller the repair that makes sense.

Can you still get the part? Makers' published commitments are narrower than people assume. Baxi says it aims to support its products for at least 10 years after they are discontinued; Vaillant says it guarantees spare parts up to 15 years after installation. We found no published period for Worcester Bosch, Ideal or Viessmann, so ask. Ofgem's ECO4 rules treat parts unavailable 'at a reasonable cost or within a reasonable timeframe' as one of three tests for a boiler that cannot be economically repaired. Give the engineer the exact model and serial number from the data plate, and ask whether the part is in stock before agreeing to a repair.

Is this a one-off or a pattern? No independent body publishes a number of breakdowns that means 'replace'. Checkatrade, a trade-lead marketplace, lists repairs becoming frequent, parts that are hard to source, repair costs adding up and rising bills as reasons to consider replacement, which is sensible but not a rule. The question to put to the engineer, in Checkatrade's words, is whether the quoted repair is expected to fully solve the issue or is a temporary fix. In our view, note every visit: repeat call-outs for one fault suggest the repairs are stop-gaps, and each is money that could have gone towards a replacement.

What would a new one actually save? Less than the sales pitch suggests, unless the old boiler is very poor. The Energy Saving Trust's figures, based on July 2026 fuel prices, put the yearly saving from replacing a D-rated boiler with a new A-rated condensing boiler plus radiator valves at £90 in a mid-floor flat, £140 in a mid-terrace, £190 in a semi and £220 in a detached house. Only a G-rated boiler, under 70% efficient, reaches £170 to £500. Our arithmetic, not EST's: against EST's £3,500 average installed cost, an E-rated semi saving £210 a year takes about 17 years to pay back. Failure makes the case, not bills.

Not sure which band yours is in? The Energy Saving Trust says your boiler is condensing, the efficient kind, if it has a plastic flue, a plastic pipe running from its base through the wall to a drain, or it is a gas boiler installed after 2005. A metal flue and no drain pipe points to an older, non-condensing boiler, where the savings above start to matter. As for the repair as a share of a replacement, there is no official percentage: we found no independent source for the 'more than half the cost of a new boiler' rule some trade sites quote. Treat it as a slogan.

What a repair costs, and what a replacement costs

Dated figures first, with one caveat: the two trade-lead marketplaces that publish repair prices give guide prices, not survey results. Checkatrade's boiler repair cost guide (updated October 2026) puts the average repair at about £300, with a range of £120 to £750 and emergency call-outs at £225 to £675; it quotes Gas Safe engineers at roughly £50 to £80 an hour plus parts. MyBuilder (updated 21 August 2026) also centres on about £300, with a range of £100 to £500. Which? surveyed 225 Trusted Trader engineers in 2025 on the ten most common faults, but its per-part averages are for members; it does say a service runs £70 to £110.

Which parts are dear? Ofgem's 2022 ECO4 heating checklist, written for installers and ex VAT, gives a relative sense: a printed circuit board about £240, a pump £200, a diverter valve £240, a gas valve £210, a fan £235 and a heat exchanger £330, with simple repairs taking one to two hours. Prices have moved since, so use the ranking rather than the numbers: a heat exchanger tops the list, and on an old boiler that is the kind of quote where the age question bites.

For a replacement, the Energy Saving Trust's average is £3,500 to replace a G-rated gas boiler with an A-rated one and radiator valves (updated 20 May 2026), and about £3,900 with full heating controls (updated 6 October 2026). Checkatrade (table updated October 2026) puts a like-for-like combi swap, supplied and fitted, at £2,500 to £4,000, and converting a system or regular boiler to a combi at about £4,000. MyBuilder (August 2026) says £2,000 to £4,000, with many paying £2,500 to £3,000 for a standard combi swap and large homes often £1,000 to £2,500 more. So a swap clusters at £2,000 to £4,000; a repair, at a few hundred pounds.

The extras are what move a quote, and Which? (September 2025) lists them: a bigger gas supply line £100 to £400, converting a heat-only or system boiler to a combi £400 to £800 on top, a hot water cylinder £350 to £1,400 depending on type, a smart thermostat £100 to £250, and a power flush on five radiators £300 to £750, averaging £500. Which? also says the like-for-like case, such as swapping one 24kW combi for another, is easier and cheaper. Relocating the boiler, changing its type or adding a cylinder is where the £4,000 figure is left behind.

What a new boiler must include in England

Since April 2018, Boiler Plus has set the rules for gas boilers fitted in existing homes in England; Scotland, Wales and Northern Ireland have their own standards. The government's Boiler Plus factsheet says a new domestic gas boiler must be at least 92% efficient on the ErP scale and fitted with a timer and room thermostat, and a combi needs one extra measure: flue gas heat recovery, weather compensation, load compensation or smart controls with automation and optimisation. A boiler below 92% does not comply even if other components raise the system label, and the rules bite only when a boiler is installed or replaced.

Ask for the system to be cleaned as well. Which? says cleaning matters so the new boiler can run efficiently, and England's current Approved Document L asks for the system to be flushed, a chemical inhibitor added and the work commissioned to BS 7593, which the Benchmark checklist can show (the 2026 edition, in force from 24 March 2027, keeps this). Guarantees can depend on it: Worcester Bosch's longer guarantees come with one of its system filters, and Vaillant says an annual service is crucial to the warranty. The Energy Saving Trust says the installer should make sure the work meets building regulations and give you the paperwork; keep it.

Getting quotes you can compare

Get at least three quotes from different installers, and only from Gas Safe registered businesses: that is the Energy Saving Trust's advice, and Citizens Advice adds to check the ID card when they arrive and ask whether they charge to come out and quote. Which? says installers often give a single figure but should still be able to explain the breakdown, even verbally. Ask each quote to name the exact boiler model and output in kW, whether it is a like-for-like swap or a relocation or change of type (Which? says swapping one 24kW combi for another is the easy, cheaper case), and which controls are included.

Then line up the extras so you compare like with like: new flue, gas pipe upsizing, condensate route, electrical work, removal of the old boiler and making good, flush type (power or chemical), inhibitor and filter, and the controls that Boiler Plus requires in England. On the guarantee, ask how long it runs, whether it covers parts and labour, who honours it, and what keeps it valid: Which? says warranties often require an annual service, and Viessmann's terms vary with registration and paid extensions. For a repair quote, Checkatrade's checklist is sound: call-out fee, labour, parts, VAT, whether the repair is guaranteed, and whether more work may follow.

Timing matters too. Checkatrade puts emergency repairs at £225 to £675, so a quote taken at 9pm in a cold snap costs more than one booked for the morning. If the house is safe and you can keep warm overnight, wait: our guides to keeping warm without heating and electric heaters cover the stop-gap, and if anyone at home is older, disabled or has a health condition, join the Priority Services Register, for extra help if the gas or power is cut off. If you want a heat pump quote alongside, Which? says to use MCS-certified installers and get several quotes; the grant is applied for through the installer.

Grants and schemes: what pays for a gas boiler, and what does not

The Boiler Upgrade Scheme does not pay for a gas boiler. GOV.UK describes it as a grant towards replacing fossil fuel heating with a heat pump or biomass boiler: £7,500 for an air or ground source heat pump, £5,000 for biomass and £2,500 for air-to-air, in England and Wales, with an extra £1,500 until March 2027 for homes on oil or LPG with no mains gas. Which? notes a like-for-like boiler swap often takes a few days where a heat pump is likely to take weeks, so a grant-funded heat pump rarely fixes this week's cold house. Our Boiler Upgrade Scheme and heat pump guides go further.

In Great Britain, the Energy Company Obligation (ECO4) can repair or replace a broken boiler for some lower-income households, but it is narrower than the adverts suggest, and the government confirmed in January 2026 that it ends on 31 December 2026, with no successor supplier obligation. Ofgem says you may qualify through certain benefits, or via a council under ECO4 Flex if household income is under £31,000 or someone has a health condition made worse by cold. The catches, from Ofgem's guidance: a condensing boiler that can be economically repaired must be repaired; like-for-like replacements are capped at 5,000 homes a year; insulation conditions apply; private tenants are generally excluded.

England's Warm Homes: Local Grant, run by councils, funds insulation, heat pumps, smart controls and solar for lower-income homes rated D to G, but the government's June 2026 guidance to councils says new gas boilers cannot be funded by it. Citizens Advice suggests asking the council about other help, a Disabled Facilities Grant if someone is disabled, and a home improvement agency for people who are older, disabled or on a low income, and warns that with any scheme you may still pay part of the cost and it may not be as quick as paying yourself. For help with bills rather than the boiler, see energy debt help.

Elsewhere the picture is more generous on paper. In Wales, the Welsh Government's Nest scheme says that if your home is without heating or hot water you may be eligible for a boiler repair or replacement (freephone 0808 808 2244). In Scotland, Warmer Homes Scotland lists a new gas boiler among eligible measures for qualifying households, but Home Energy Scotland says you cannot get funding for completed work, so get assessed before paying anyone. In Northern Ireland, the Boiler Replacement Scheme has closed; the Housing Executive's Affordable Warmth Scheme can replace a boiler over 15 years old for qualifying households earning under £23,000, subject to funding (0800 111 44 55).

If you rent

The decision and the bill are the landlord's. In England, section 11 of the Landlord and Tenant Act 1985 makes landlords keep heating and hot water installations in repair and proper working order, and Shelter Legal says a tenancy term cannot shift it onto you. It adds that a landlord 'is not obliged to replace an item where it is possible to repair' and may choose the cheaper option. So you cannot usually insist on a new boiler if a repair works, but repeat failures, missing parts or a safety label are the landlord's to resolve; if an appliance is disconnected, the HSE says they must provide emergency heating.

Report the fault in writing, keep paying rent, and pass on any warning notice the same day. Grant routes mostly do not apply to tenants for boiler work: Ofgem's ECO4 guidance generally excludes boiler repair and replacement in privately rented homes, and Warmer Homes Scotland will not fund what the Repairing Standard already obliges a landlord to provide. Timescales, Awaab's Law for social tenants, and the rules in Scotland, Wales and Northern Ireland are in the renting sections of our winter boiler guide.

Repair or replace: the short version

Nobody independent publishes a formula, so this is our reading of the sources above, written for a household paying its own bill. The honest default for a boiler under about ten years old with a minor fault is to repair it.

Repair if: the boiler is under about ten years old; the fault is a single part such as a pump, valve or sensor, and the part is in stock; the quote sits in the £100 to £750 repair range the marketplaces report rather than a large share of a £2,000 to £4,000 replacement; it is the first failure, or the first in years; it is a condensing boiler (plastic flue, installed after 2005), so the efficiency gain from a new one is small; or it is still under guarantee, in which case call the maker or installer before paying anyone.

Replace if: the engineer says the part is no longer available, or only at a price and delay that make no sense; it has failed repeatedly and each repair has been a stop-gap; the quote needs a heat exchanger or several parts on a boiler past about twelve years; it is an old non-condensing boiler rated G (under 70% efficient), where the Energy Saving Trust's savings reach £170 to £500 a year; or a safety label cannot be cleared by an affordable repair. If money is the obstacle, go back to the schemes above before you agree to anything, and if you rent, hand the whole question to your landlord.