How much does a combi boiler replacement cost?

Like-for-like combi swap: £2,000–£3,500

Replacing an old combi with a new combi in the same spot is the cheapest boiler job there is: typically £2,000–£3,500 installed in 2026 (estimate, checked October 2026). The boiler unit itself is £800–£1,500 of that depending on brand and warranty length; the rest is a day's labour, the flue, a system flush, and certification.

That range assumes a straightforward swap — same location, no major pipework changes. Prices cluster around £2,400–£2,800 for the big mid-range brands (Worcester Bosch, Vaillant, Ideal) with 7–10 year warranties. Budget brands shave a few hundred off; premium models with 10–12 year warranties add a few hundred.

Conversions cost more: £3,000–£4,500

Switching boiler type — say from a regular boiler with tanks to a combi, or a system boiler to a combi — is a bigger job: roughly £3,000–£4,500 (estimate). The extra money covers removing tanks and cylinders, reworking pipework, and often relocating the boiler or flue. Allow 2–3 days instead of one.

Conversions can still be worth it: ditching the airing-cupboard cylinder frees real space, and combis suit smaller households well. But if your regular boiler works fine and you like your stored hot water, "convert because combis are modern" is not by itself a reason to spend the extra.

What's included in a proper quote?

Compare quotes on identical scope, or you will compare nonsense. A complete replacement should itemise: the boiler unit (named model), flue kit, labour, a system power flush (old sludge kills new boilers — skipping the flush to save £300 is false economy), a new thermostat/controls, condensate pipework run to a drain, Gas Safe registration of the install, and the warranty terms in writing.

Watch for the classics: quotes that exclude the flush, vague "controls included" lines that turn out to be a £30 basic thermostat, and warranties that require annual servicing by that same firm to stay valid. Get three written quotes minimum — boiler pricing varies wildly between firms for identical hardware.

Repair or replace? The maths

A decent rule of thumb: repair if the boiler is under 10 years old and the fix is under ~£400. Replace if it is 12–15+ years old, if you are calling engineers out more than once a year, or if parts are getting scarce and expensive.

Also factor efficiency: a 15-year-old non-condensing boiler might run at 70% efficiency versus 90%+ for a new condensing combi. On a £1,200-a-year gas bill, that 20-point gap is worth roughly £200+ a year (estimate) — which quietly pays for a chunk of the replacement over its life. Our boiler cost calculator prices your exact scenario.

Are there grants for a new gas boiler?

Honest answer: no general grant exists for a like-for-like gas boiler replacement. The Boiler Upgrade Scheme's £7,500 is for heat pumps, not gas boilers. ECO4 can fund boiler replacements, but only for eligible low-income households — and it ends on 31 December 2026. Anyone cold-calling about "free boilers for everyone" is running a lead-generation funnel, not a government scheme. Check what you genuinely qualify for with our grant eligibility checker.

What's included in a good quote

A proper combi replacement quote should itemise: the boiler itself, flue (new flues are usually needed), a magnetic system filter, heating controls (at minimum a programmable thermostat — smart controls add £150–£250, estimate), a chemical flush of the system, condensate pipework routed properly to a drain, Gas Safe registration, and the Building Regulations compliance notification. Labour for a straightforward swap is typically a day's work.

Watch for the extras that turn a £2,500 quote into £4,000: powerflushes on sludged systems, relocating the boiler, upgrading the gas pipe from the meter, and scaffolding for awkward flue routes. None are scams — they're legitimate costs — but they should be in the quote before work starts, not discovered halfway through.

Signs yours is dying

Don't wait for a winter breakdown to force the decision at emergency rates. Warning signs: kettling (a rumbling like a kettle boiling — limescale on the heat exchanger), frequent lockouts needing resets, radiators that never quite get hot, steadily rising gas bills for the same usage, and any yellow or orange flame instead of crisp blue. A boiler limping past 12–15 years with mounting repair bills is usually cheaper to replace than to keep reviving.

FAQs

How much does it cost to replace a combi boiler in the UK?

Typically £2,000–£3,500 installed for a like-for-like swap in 2026 (estimate). Conversions from other boiler types run £3,000–£4,500.

How long does a combi boiler replacement take?

Usually one day for a straight swap; 2–3 days for conversions with new pipework or flue relocation.

Should I repair or replace my boiler?

Repair under 10 years old with a sub-£400 fix; replace at 12–15+ years, frequent breakdowns, or scarce parts.

What should a boiler quote include?

Named boiler model, flue, labour, power flush, controls, condensate pipework, Gas Safe registration and written warranty terms.

Are there grants for replacing a gas boiler?

No general grant. ECO4 covers eligible low-income households until 31 December 2026; the Boiler Upgrade Scheme is heat pumps only.