How Much Does a New Combi Boiler Cost in 2026? (UK)
A new combi boiler costs £1,800–£4,500 supplied and fitted in 2026, depending on the brand, output and how much work the job needs. A like-for-like swap in the same spot is cheapest at £1,500–£2,500, a mid-range install lands around £2,500–£3,500, and a premium boiler with a conversion or relocation reaches £4,000–£5,000+. Premium brands cost more but carry 10–12 year warranties when fitted by an accredited installer. The final figure hinges on the boiler, the conversion work, flushing and your region. Here's the full breakdown.
Combi boiler cost by job type (2026)
| Job type | Typical cost (fitted) | Notes |
|---|---|---|
| Like-for-like swap (same location) | £1,500–£2,500 | Old combi out, new combi in the same spot |
| Standard combi replacement | £2,000–£3,500 | New boiler, filter, flush, controls |
| System boiler to combi conversion | £2,800–£4,000 | Cylinder removed, pipework altered |
| Back boiler to combi conversion | £3,000–£4,500 | Fireplace boiler removed, new flue run |
| Premium boiler + relocation | £4,000–£5,000+ | New position, extra pipe and flue work |
Ranges assume a domestic gas combi from a mainstream brand. London and the South-East typically sit 10–20% above these figures. A power flush, new radiators or a gas-pipe upgrade add to the totals below.
Combi boiler cost by job type — 2026
Typical fitted totals, plus the London uplift.
Mainstream gas combi, fitted. Source: BestBuilders 2026 quote data · 519 UK towns
Where the money goes
| Element | Share of budget | Notes |
|---|---|---|
| Boiler unit | 40–55% | Brand and output are the biggest single variable |
| Labour (Gas Safe fitter) | 25–35% | 1–3 days depending on swap vs conversion |
| Flushing & filter | 8–15% | Power flush and a magnetic system filter |
| Flue, pipework & fittings | 8–15% | New flue run and gas/condensate pipe |
| Controls | 4–10% | Programmer, thermostat or smart control |
What is included at each price point
| Specification | Cost (2026) | What you get |
|---|---|---|
| Budget combi (Ideal, Baxi), fitted | £1,800–£2,500 | Reliable boiler, 5–7 year warranty |
| Mid-range combi (Worcester/Vaillant entry), fitted | £2,500–£3,500 | Quieter, longer warranty options |
| Premium combi (Greenstar / ecoTEC), fitted | £3,000–£4,500 | 10–12 year warranty, top reliability |
| Power flush | +£400–£700 | Removes sludge, protects the new boiler |
| Magnetic system filter | +£120–£200 | Now standard on a good install |
| Boiler relocation | +£400–£1,000 | New position, extra pipe and flue |
| New radiator (each) | £150–£350 | Supply and fit while the system is drained |
| Smart thermostat | +£150–£300 | Hive, Nest or Tado control |
| Gas pipe or flue upgrade | +£150–£500 | Where the existing run is undersized |
What size combi do you need?
| Home | Typical output | Notes |
|---|---|---|
| Flat or small house, 1 bathroom | 24–28kW | Lower demand, cheaper unit |
| Typical 3-bed house, 1 bathroom | 30–35kW | The most common choice |
| Large house, 2+ bathrooms | 35–42kW | Higher hot-water flow rate needed |
Bigger is not better: an oversized combi cycles on and off, wastes gas and wears faster. A good installer sizes the boiler on a heat-loss calculation and your hot-water demand, not a rule of thumb. See our what size boiler do I need guide.
Regional price differences
| Region | Against UK average |
|---|---|
| London | +15–20% (labour, parking) |
| South East and commuter towns | +10–15% |
| South West and Eastern England | +5–10% |
| Midlands | Around the average |
| North West, Yorkshire | −5–10% |
| North East, Scotland, South Wales | −8–12% |
The same mid-range combi swap priced at £2,600 in the Midlands can pass £3,200 in London before any spec change. Always judge quotes against local rates — our boiler replacement cost guide breaks the bands down further.
How the job runs (1–3 days on site)
- Survey & sizing — the installer checks the system, sizes the boiler on heat loss and hot-water demand, and quotes a fixed price.
- Isolation & strip-out — day 1: gas and water isolated, old boiler (and cylinder or back boiler on a conversion) removed.
- Flush — a power flush or chemical flush clears sludge before the new boiler goes on.
- Fit & pipework — new combi, flue, condensate, magnetic filter and any altered pipework installed.
- Commissioning — the fitter commissions the boiler, completes the Benchmark checklist, registers the warranty and notifies Building Control via Gas Safe.
Choosing the installer: checklist
- The fitter is Gas Safe registered — check the card and the register; this is a legal requirement for gas work.
- Manufacturer-accredited (e.g. a Worcester Accredited Installer) so you get the full 10–12 year warranty.
- The quote includes a power flush or system flush, a magnetic filter and the Benchmark checklist.
- The boiler is sized on a heat-loss calculation, not guessed from the old one.
- A written fixed-price quote and warranty registration — never a cash-only, paperwork-free deal.
- Three itemised quotes on the same boiler and scope so the numbers are genuinely comparable.
Red flags
- The fitter is not Gas Safe registered — walk away; illegal gas work is dangerous and uninsurable.
- No flush quoted on an old system — sludge will damage the new boiler and can void the warranty.
- An oversized boiler pushed without a heat-loss calculation — it wastes gas and wears out sooner.
- No Benchmark checklist or warranty registration — you lose your guarantee.
- Large cash deposit requests or “VAT-free” offers with no paperwork.
FAQs
Related guides
- How much does a new boiler cost in 2026?
- Combi boiler prices UK
- Combi vs system vs heat-only
- What size boiler do I need?
- Boiler replacement cost guide
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