If your boiler dies in February, you don't have time for the heat pump conversation. You need heat in 48 hours and what you're getting is a like-for-like gas combi from whichever Gas Safe engineer can fit you in. That's roughly half of UK boiler replacements: emergency, not planned.
The other half — the planned ones, where the existing boiler is wheezing through one more winter and you've got 6-12 months to think — these are where the actual choice opens up. And in 2026 the choice is genuinely interesting, because the £7,500 Boiler Upgrade Scheme grant has narrowed the cost gap between gas and heat pump enough that the maths is no longer a foregone conclusion.
The honest framing: if you're staying long-term in a reasonably insulated house, get a heat pump quote alongside the gas quote. The maths might surprise you. If you're moving in three years, or your house is uninsulated, or you can't face a 3-day install, the gas boiler is fine.
The boiler that actually works in most UK homes
For 80% of UK homes, the right gas boiler in 2026 is a Worcester Bosch Greenstar i at £1,800-£2,800 installed. There's nothing exciting to say about it. Worcester Bosch dominates the UK market for the same reason Toyota dominates Japanese cars: the things mostly work, parts are stocked everywhere, every plumber knows them, and the warranty is honoured.
The 10-year standard warranty (with annual servicing) is genuinely useful. The cheaper boilers (Ideal, Baxi) have shorter warranties and slightly more variable longevity. The premium boilers (Vaillant ecoTEC, Viessmann Vitodens) edge Worcester on efficiency by 1-3% and on quietness, neither of which transforms the daily experience.
The price spread on the same job tells you something:
- Ideal Logic combi: £1,500-£2,500 installed
- Worcester Bosch Greenstar i: £1,800-£2,800
- Vaillant ecoTEC plus: £2,000-£3,000
- Viessmann Vitodens 100-W: £2,500-£3,500
For most UK households the £500-£1,000 difference between Ideal and Viessmann doesn't pay back through energy savings. Choose by who installs them well in your area, not by brand.
Combi, system, or regular: a decision that's actually still alive
Most UK boiler replacements default to combi (no hot water tank, hot water on demand). For most households this is correct. The exceptions matter:
A combi boiler can supply about 12-15 litres/minute of hot water, comfortably for one shower. Two showers running simultaneously, or a shower plus a bath fill, will struggle. Households with multiple bathrooms running in parallel are a genuine system-boiler use case.
Households planning to install solar PV with a hot water diverter (excess solar heats the cylinder rather than exporting to the grid) need a tank, which means a system boiler not a combi.
Households where mains water pressure is poor (1.5-2 bar) might struggle with combi flow rates and benefit from a system boiler with a cold water storage tank that gives more consistent pressure.
Most other households are right with a combi.
The traditional "heat-only" or "regular" boiler with hot water tank in airing cupboard and cold water tank in loft is now mostly a like-for-like replacement only — if you've already got the system, replacing with the same configuration is fine. Don't actively choose this configuration for a new install.
The heat pump alternative, honestly
The reason heat pump conversations confuse people is that the maths depends on three variables most homeowners haven't checked: insulation level, radiator sizing, and electricity tariff.
Net installed cost (after the £7,500 BUS grant) for a typical 8kW air source heat pump on a 3-bed semi: £3,500-£8,500. That's £1,500-£4,000 above a like-for-like Worcester Bosch combi. The premium is recouped over 10-15 years if running costs are 15-25% lower, which they are only on the right tariff.
The honest variables that decide whether the heat pump wins for your specific house:
Insulation. Heat pumps run flow temperatures of 40-55°C versus 60-80°C for gas. In a poorly insulated house, the lower flow temperature can't keep up with heat loss, and the system runs constantly without reaching set point. Insulate first. Then quote.
Radiator sizing. A radiator sized for 70°C gas-boiler flow is undersized for 50°C heat-pump flow. Most heat pump installs include 2-6 radiator upgrades in the price; if your installer doesn't mention this, the quote is incomplete.
Tariff. Octopus Cosy at 12.5-15p/kWh during 6 cheap-rate hours per day is what makes the heat pump cheap to run. On a standard 28p/kWh tariff, the heat pump's running cost is similar to gas. Switch to Cosy on commissioning day, not later.
House size. Heat pumps scale to about 16kW comfortably for domestic use. Genuinely large houses (250m²+) with high heat loss may need a 20kW+ system, which gets expensive enough that the gas comparison favours gas.
For most UK semi-detached homes with reasonable insulation, the heat pump is now a defensible choice. For poorly insulated detached houses, fix the insulation before quoting either heating system.
There's a longer treatment in the heat pump article if this is the path you're seriously considering.
How a quote should look
A reputable boiler replacement quote includes:
- The specific make and model of boiler (not just "combi boiler")
- Flue type and routing
- Power flush of existing radiators (£300-£500 — important; old sludge in the system will damage a new boiler)
- New thermostat or transfer of existing
- Magnetic system filter (£80-£150 — collects debris before it reaches the new boiler; should be standard)
- Manufacturer warranty registration (manufacturer's warranty often requires the installer registers the install)
- Building Notice / Building Regulations notification (legally required for boiler installs; included in the quote of any reputable installer)
- Disposal of old boiler
Three quotes minimum for any planned replacement. The spread on the same job typically runs 20-40%, which means the cheapest quote and the most expensive quote on the same boiler are often £800-£1,500 apart.
For heat pumps, the additional items in the quote should include the heat-loss calculation, radiator upgrades by room, hot water cylinder, electrical work, BUS grant application, and MCS certification. A heat pump quote that doesn't show a heat-loss calc by room is a guess; reject it.
Annual servicing is the hidden cost people forget
A new boiler must be serviced annually to maintain manufacturer warranty. Costs:
- Standalone annual service: £80-£120
- Service contract with parts cover: £150-£300/year
- Manufacturer's plan (Worcester Bosch, Vaillant): £200-£350/year, sometimes including the first year free
For UK homeowners who want simplicity: a manufacturer's annual plan removes the disputes about warranty cover and ensures servicing happens. For UK homeowners willing to phone an independent engineer: a single annual service plus paying out-of-pocket for any repairs is usually cheaper.
Heat pumps need annual servicing too. Costs are similar (£100-£200 typical) but the engineer pool is smaller; book early.
What to do if the existing boiler is fine
The genuine answer most home-improvement articles avoid: don't replace a working boiler.
The economic case for proactive boiler replacement is weak. A working boiler that's 12-15 years old will probably keep working for another 5-10 years with annual servicing. Modern condensing boilers are 90-94% efficient versus 75-85% for pre-2005 boilers, so there are some running cost savings, but they don't recoup a £2,500 install in less than 8-10 years for typical UK heating bills.
Replace when:
- The boiler has had multiple expensive repairs (£200+ jobs more than once a year)
- A major component (heat exchanger, fan) has failed
- The boiler is genuinely past serviceable life (20+ years, parts unavailable)
- You're doing a full home renovation where it makes sense to upgrade as part of the project
- You want to switch heating type (gas to heat pump) and have decided this is the right window
Don't replace because:
- A salesperson said your boiler is "old"
- Annual servicing turned up a routine adjustment
- You read an article about modern boilers being more efficient
What I'd actually do, by scenario
Boiler died in February, no time for choices. Phone two Gas Safe engineers, ask for a same-week quote on a Worcester Bosch Greenstar i or equivalent. Pick the one available. £1,800-£2,800 installed. Get on with life.
Boiler is end-of-life, planned replacement, you're staying 10+ years. Get three quotes for a like-for-like gas replacement. Get one quote for an air source heat pump with the BUS grant included. Compare net costs and 5-year running costs. If the heat pump quote comes back competitive on net cost and the house is reasonably insulated, take it. If not, gas combi.
Boiler is end-of-life, you're moving in 2-3 years. Gas combi. The heat pump premium doesn't recoup before you sell. The next owner will deal with their own heating choice.
You're in the middle of a renovation. Now is the right time for a heat pump. The radiator upgrades and electrical work fold into the renovation; the disruption is contained. Specify it in the renovation scope.
Listed building or conservation area. Specialist advice. Some heating decisions are constrained by building regs you wouldn't normally meet. A few specialist installers know this territory; ask the local conservation officer for recommendations.
The choice that matters most is whether you've insulated the house. Without that, neither boiler nor heat pump will perform well. With it, either can; the choice between them becomes about your time horizon and your tolerance for the more involved heat-pump install.
This article is general consumer information about UK boiler replacement, not building services advice. UK heating decisions involve significant capital and safety considerations; use Gas Safe registered installers; verify MCS certification for heat pumps.
Affiliate disclosure: Morningfold has affiliate partnerships with Worcester Bosch, Vaillant, Viessmann, Ideal, and several UK heating installer marketplaces. See editorial standards.