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A modern condensing combi boiler is the latest gas heating system with up to 98% efficiency. In the UK, the new combi boiler price can be in the region of between £1,500 and £4,500 with fitting, while the average homeowner in the UK spends about £3,800 for supply and installation.
However, prices can significantly vary depending on the size of the boiler, its brand, fuel type, and complexity of the installation. That is precisely why we have compiled this guide to help UK households understand what costs they are looking at if they decide to upgrade and further discuss ways to reduce those costs.
What Drives Your Combi Boiler Price?
Three factors determine how much it costs for you: First, the heating demand of your property, a bigger house, a bigger boiler, and a bigger bill. The second factor is the brand you choose, and yes, quality costs. And thirdly, the complexity of the installation: a simple swap takes four hours; a full conversion takes three days.
Want the short version? Here’s your pricing snapshot:
| Property Size | Output Needed | Typical Cost (Including Installation) |
|---|---|---|
| 1-2 bedrooms | 24-27 kW | £1,500 – £2,500 |
| 3 bedrooms | 25-30 kW | £2,200 – £3,200 |
| 4+ bedrooms | 30-35 kW | £2,500 – £4,500 |
Modern condensing combi boilers reach 90-98% efficiency. That’s real money back in your pocket.
Air Source Heat Pump Grants
Combi Boiler Prices by House Size
Size matters more than most installers will admit. Get this wrong and you’ll be freezing in winter or wasting hundreds on an oversized kit.
What Size Boiler for a 2-Bed House?
Small homes need 24-27 kW. That’s all. You’ve got limited heating demand, probably one bathroom, maybe ten radiators max.
- Budget range: £1,500 – £2,500 fitted
- Mid-range models: £2,000 – £3,000 fitted
- Premium brands: £2,500 – £3,500 fitted
Go budget if you’re selling within five years. Go premium if you’re staying put.
What Size Boiler for a 3-Bed House?
The sweet spot: most UK homes sit here and need 25-30 kW output. You’re balancing performance against cost, and frankly, this is where quality matters most.
The standard range sits at £1,800 to £4,000 fitted, but let’s get real—you’ll pay between £2,200 and £3,200 for anything worth installing. Units by Worcester Bosch land between £2,200 and £2,800 when properly installed.
Why the spread? Installation complexity: straight swap versus full conversion.
What Size Boiler for a 4-Bed House?
Larger properties demand 30-35 kW minimum. You’re running 15+ radiators, multiple bathrooms, maybe two showers going simultaneously. Undershoot here and you’ll regret it every January.
Expect to pay £2,500-£4,500 for supply and fitted. High-output models nudge £5,000, but they’ll actually deliver when everyone’s home. Premium units handle the load without breaking a sweat.
Combi Boiler Prices by Brand
Three manufacturers dominate. They’ve earned it.
Worcester Bosch: The UK Default
Number one seller for a reason: their warranties go up to 12 years, their service network is everywhere, and they rarely fail.
| Model | Boiler Only | Fitted Price |
|---|---|---|
| Greenstar 1000 | £675 – £720 | £1,895 – £2,200 |
| Greenstar 2000 | £950 – £1,050 | £2,150 – £2,450 |
| Greenstar 4000 | £1,150 – £1,250 | £2,400 – £2,700 |
| Greenstar 8000 | £1,550 – £1,950 | £2,700 – £2,950 |
You’re paying for peace of mind. Worth it? Usually.
Vaillant: German Engineering Done Right
Great efficiency. Ten-year warranties. Quieter than Worcester Bosch, if that’s something important to you.
- EcoFIT pure 825: £907 (unit only) or £1,707 – £2,207 fitted
- ecoTEC plus 832: £1,770 (unit only) or £2,570 – £3,070 fitted
- Full ecoTEC range: £1,100 – £2,600 supply and fit
Slightly cheaper than Worcester. Marginally better efficiency ratings. Your call.
Ideal: British Value Play
Good quality, lower prices, solid warranties on premium models. The Logic range delivers reliable heat without the premium pricing.
- Logic Combi range: £625 – £1,409 (boiler only)
- Logic² Max 30 kW: £1,026 (unit only) or £1,826 – £2,326 fitted
- Complete range spans: £625 – £2,780
Perfect for budget-conscious buyers who still want quality.
Installation Costs by Conversion Type
Here’s where costs explode or stay reasonable. Installation type determines everything.
Combi to Combi: The Easy Swap
Simple. Fast. Cheap. You’re replacing like-for-like, using existing pipework, same-day service.
- Total cost: £2,500 – £4,000 (supply and fit)
- Time needed: 4-6 hours
- Additional costs: None
This is your baseline. Everything else costs more.
System to Combi: Moderate Complexity
You’re changing the heating system configuration. Pipework modifications required. Takes longer, costs more.
Around £4,000 total for supply and installation. Plan for up to three days of downtime. Not ideal mid-winter.
Conventional to Combi: The Big Upgrade
Ripping out tanks and cylinders. Freeing up space. Modernising completely.
Expect £4,000 average, roughly two days’ work. Includes removing your old cylinder and associated pipework. You’ll gain an airing cupboard back.
Back Boiler to Combi: Maximum Effort
The toughest conversion. Old back boilers hide behind fireplaces, making access difficult. Full decommissioning adds £500 to £1,000 extra.
Total cost: £3,000 – £4,500. But here’s your reward—up to £330 annual savings on energy bills for detached houses. Pays for itself within ten years.
Fuel Type Price Variations
Your fuel choice shapes everything: upfront cost, running cost, and installation complexity.
| Fuel Type | Unit Cost | Installed Cost | Annual Running Cost |
|---|---|---|---|
| Gas | £600 – £3,000 | £1,600 – £6,000 | £1,440 (3-bed home) |
| Oil | £1,300 – £4,000 | £3,000 – £7,500 | £1,200 – £2,000 |
| Electric | £500 – £3,050 | £1,500 – £4,000 | £2,000 (1-2 bed) |
Gas remains the cheapest long-term. Electric works for small properties. Oil fills the gap for rural homes without a gas supply.
Combi Boiler Running Costs
Purchase price is one thing. Running costs determine value.
What Does Gas Heating Actually Cost?
Current UK energy rates mean:
- 24 kW boiler: £0.96 per hour at full load
- 30 kW boiler: £1.20 per hour at full load
- Annual heating: £840 – £1,200 for average usage
Real efficiency makes a real difference. A-rated boilers achieve 90-94% efficiency. Older G-rated units? Maybe 60-70%.
Replace that old boiler and save up to £490 annually. Your payback period? Three to five years. Then pure savings for the next 15-20 years.
Service and Maintenance Costs
Annual servicing isn’t optional. It’s insurance against expensive breakdowns.
Basic service runs £70 to £150 yearly. Most engineers charge £90 to £100. London? Add 20-30%, so £120 to £140.
Should you get a service plan? Not for new boilers. Pay annually and pocket the difference. Once your warranty expires, maybe consider coverage. But new units rarely fail within five years.
Additional Costs Worth Knowing
Professional installations include hidden extras you should budget for:
Essential additions:
- Magnetic filter: £100 – £200 (protects your investment)
- Smart controls: £150 – £400 (improves efficiency)
- Flue extensions: £200 – £700 (if needed)
- Pipework modifications: £200 – £800 (depends on layout)
Location surcharge:
- London/Southeast: 15-20% above the national average
- Northern England: 10-15% below average
- Difficult access: Extra £200 – £500
Gas Safe registration comes standard with legitimate installers. Building regulations compliance? Also included. Both protect your warranty.
The Bottom Line
Modern combi boilers cost £1,500 to £4,500 installed. You’ll save money long-term through improved efficiency. Most systems last 15-20 years with proper maintenance.
Choose based on your needs, not marketing hype. Size appropriately. Pick quality brands. Use Gas Safe engineers. Simple.
Frequently Asked Questions
Here’s what actually matters:
Property Size | Typical Output | Reality Check |
2-bed flat | 24-27kW | 8-10 radiators, 1 bathroom |
3-bed semi | 28-30kW | 10-12 radiators, 1-2 bathrooms |
4-bed detached | 32-35kW | 13-15 radiators, 2+ bathrooms |
5-bed+ | 35kW+ | Get a proper heat loss calc done |
A poorly insulated 2-bed Victorian terrace needs more heat than a modern 3-bed new-build. Your radiator count, insulation quality, and simultaneous hot water demand determine sizing.
Combi-to-combi replacement takes 4-6 hours if the pipework’s sound and positioning stay identical. While converting from conventional to combi? 2-3 days minimum. As you’re removing tanks, rerouting pipework, and upgrading electrics. Remember, anyone promising faster is cutting corners. However, back boiler replacement takes 1-2 days, depending on decommissioning complexity and whether your living room wall needs replastering afterwards.
The government isn’t handing out cash for standard boiler replacements anymore. ECO4 targets fuel-poor households with pre-1990s boilers rated D or below. Strict eligibility. Means-tested benefits required. Some local authorities run targeted schemes for vulnerable households. Check your council’s energy team if you’re over 65 or claiming benefits.
A £2,500 boiler investment with £400 annual savings pays back in 6-7 years. Warranty outlasts payback.
- G-rated to A-rated upgrade: Up to £490 annually for an average 3-bed semi-detached. That’s 25-30% fuel reduction from 65% efficiency to 92%+.
- Back boiler replacement: £330 yearly savings are typical. Those ancient systems run 55-60% efficient on good days. New combis deliver 40% improvement.
All hit 92-94% ErP efficiency. Performance differences? Negligible in real-world use.
Worcester costs more, but 12-year coverage means a lower annualised ownership cost than 5-year budget brands needing replacement sooner.
Vaillant offers near-identical performance at 15% less. German engineering, competitive pricing, proper UK support network.
Ideal suits cost-conscious buyers wanting 10-year protection without premium branding. Logic Max range punches above its price point.
