New Combi Boiler Cost in the UK: Full 2026 Price Guide (Including Installation)

When the boiler dies in January, you don’t have time to shop around elegantly — but knowing the numbers in advance saves you from panic-buying an overpriced unit. Here’s how much a new combi boiler costs including installation in the UK right now.

The headline figures

• Budget combi (boiler + installation): £1,800–£2,400
• Mid-range (Worcester Bosch, Vaillant, Ideal): £2,400–£3,200
• Premium / high-output: £3,200–£4,500
• London & South East: add £300–£600 to the above

The boiler unit itself is typically £900–£1,800 of that; the rest is labour, flue, controls, chemicals (inhibitor, filter) and certification. A straight like-for-like swap in the same location is cheapest; moving the boiler to a new position adds £300–£800.

What affects the price?

• Brand: Worcester Bosch and Vaillant command a premium (and hold value); Ideal and Baxi offer strong warranties for less. All are decent — the installer matters more than the badge.
• Output (kW): a 1-bed flat needs ~24kW; a 4-bed house with 2 bathrooms needs 30–35kW. Oversizing wastes money; undersizing means weak showers.
• System conversion: switching from a conventional boiler + tanks to a combi adds £500–£1,000 (removing tanks, upgrading pipework).
• Flue changes: a new flue route or vertical flue adds £200–£500.
• Smart controls: a smart thermostat fitted at install adds £150–£250 — worth considering (see are smart thermostats worth it?).
• Magnetic filter & flush: a system powerflush (£300–£500) is often recommended on older systems — get it itemised, not bundled opaquely.

Getting quotes without getting ripped off

1. Get 3 quotes minimum — from Gas Safe registered installers (verify at gassaferegister.co.uk).
2. Demand itemised quotes: boiler model, labour, flue, controls, filter, flush, certification — separately priced.
3. Check the warranty: 5 years is standard; 10-year warranties (Worcester Bosch, Vaillant via accredited installers) are worth real money.
4. Ask about the Benchmark logbook — a proper installer completes this; it’s your warranty proof.
5. Beware the “today only” discount — classic pressure tactic. A genuine quote is valid 30 days.
6. Check reviews on Checkatrade or Trustpilot, and ask for local references.

Repair vs replace: the decision

As a rule of thumb:

• Repair if the boiler is under 8 years old and the fix is under £400.
• Replace if it’s 12+ years old, needs a £500+ repair, or breaks down yearly. Old boilers run at 70–80% efficiency versus 90%+ for new — the fuel saving alone is £150–£300/year.
• Between 8–12 years: get an honest engineer’s opinion. Some 10-year-old Worcesters have years left; some 9-year-old budget units are done.

Finance and grants

• Many installers offer 0% finance over 12–24 months — useful for spreading £2,500.
• The Boiler Upgrade Scheme covers heat pumps, not gas boilers — but if you’re considering ditching gas, grants of £7,500 exist for heat pumps.
• ECO4 may fund replacements for low-income households on benefits — check eligibility on gov.uk.

How long does installation take?

A straightforward combi swap: 1 day. A system conversion: 2–3 days. You’ll be without heating/hot water during the work — in winter, ask the installer to schedule to minimise this (some fit the new boiler before removing the old).

The bottom line

Budget £2,200–£3,000 for a quality combi boiler fully installed (more in London), from a Gas Safe installer with an itemised quote and a 7–10 year warranty. Get three quotes, don’t be rushed, and remember: the cheapest quote with a 2-year warranty is usually the most expensive boiler you’ll ever buy. For keeping it healthy afterwards, see how often to service your boiler.

Combi vs system vs regular: are you buying the right type?

Before you price a combi, make sure a combi is right. Combi boilers (heating + instant hot water, no tanks) suit most 1–3 bedroom homes — they’re compact, efficient and cheap to install. But they’re wrong when: you have 2+ bathrooms used simultaneously (combis can’t run two showers at full pressure — flow rate is the limitation), low mains water pressure (combis need decent pressure; under ~1 bar dynamic, consider a system boiler with unvented cylinder), or large households with high hot-water demand.

System boilers (+ unvented hot water cylinder) cost £2,800–£4,500 installed — more, but they deliver proper multi-bathroom performance. Regular (heat-only) boilers suit homes with existing traditional systems and loft tanks. A good installer assesses your hot water demand, mains pressure and flow rate before recommending — if they quote a combi without testing your water pressure, get another quote. The wrong boiler type is a 15-year mistake.

New boiler FAQs

How long do combi boilers last? 12–15 years typically with annual servicing; 10 years without. Premium brands (Worcester Bosch, Vaillant) often reach 15–18 years. Budget brands: 8–12 years.

What size combi do I need? Rough guide: 24–27kW for flats/2-bed houses (1 bathroom); 28–32kW for 3-bed (1–2 bathrooms); 32–40kW for 4+ bed or 2 bathrooms. But hot water flow rate (litres/min) matters more than kW for combis — ask for the DHW flow rate, not just the heating output.

Should I switch to a heat pump instead? If your home is well-insulated with radiators sized for lower flow temperatures, a heat pump (£7,500 grant via the Boiler Upgrade Scheme) can work brilliantly — but it’s a bigger project (often £10,000–£15,000 total). For most existing homes needing a quick replacement, a modern gas combi remains the pragmatic choice.

Can I install it myself / get a mate to do it? No — gas boiler installation legally requires Gas Safe registration, and the Benchmark commissioning paperwork (needed for warranty and building regs) must be completed by the installer. DIY gas work is illegal and invalidates home insurance.

When’s the cheapest time to buy? Summer — installers are quieter, manufacturers run promotions, and you’re not paying emergency premiums. A January breakdown replacement can cost 20–30% more than a planned August install.

The quote comparison checklist

Three quotes in hand — now compare them properly. Checklist: boiler make and exact model (not just “Worcester” — which one? The 2000, 4000 and 8000 series differ enormously in price and quality); kW output (matched to your home — oversized wastes money, undersized disappoints); warranty length and terms (5 vs 10 years; who’s registering it? is annual servicing by any Gas Safe engineer accepted, or only accredited installers?); what’s included (flue, controls, magnetic filter, system flush, inhibitor, Benchmark logbook, building regs notification); what’s excluded (making good plasterwork? upgrading the gas pipe? condensate drain routing?); timescale (when can they start, how many days?); payment terms (deposit %, balance on completion — never pay in full upfront).

Red flags in quotes: no model specified (“a new combi” — which one?), no mention of flush/filter (essential on old systems — their absence suggests corner-cutting), price valid “today only” (pressure tactic — walk away), cash discount offered unprompted (tax evasion flag), no Gas Safe number on the paperwork. The deciding factor between similar quotes: reviews and references — a £200 cheaper quote from an unknown is worse value than a fairly-priced quote from a highly-reviewed local installer. The boiler lasts 15 years; the installer relationship matters.