How Much Does a Combi Boiler Cost?
Updated 28 March 2026
Combi boiler prices by output size, top brands, running costs, and what happens on installation day.
Quick Answer
New combi boiler supplied and fitted: £1,800 to £3,500.
Boiler unit only
£600-£1,500
Budget brands to premium (Worcester, Vaillant)
Installation labour
£800-£2,000
Depends on complexity and location
Cost by Output Size
Output is measured in kilowatts (kW). Getting the right size matters. Oversizing wastes money. Undersizing means lukewarm showers.
| Output | Best for | Installed price |
|---|---|---|
| 24kW | 1-2 bed flat, 1 bathroom | £1,800-£2,500 |
| 28kW | 2-3 bed house, 1 bathroom | £2,000-£3,000 |
| 30kW | 3 bed house, 1-2 bathrooms | £2,200-£3,200 |
| 35kW | 4 bed house, 2 bathrooms | £2,500-£3,500 |
| 40kW+ | Large house, multiple bathrooms | £3,000-£4,000 |
Prices include supply, installation, removing the old boiler, and flue. London and South East typically adds £200 to £400 due to higher labour rates.
Top Combi Boiler Brands
Most Gas Safe engineers will recommend Worcester Bosch or Vaillant. Both are solid choices with strong warranties and good parts availability.
Worcester Bosch
£800-£1,500
The most popular brand in the UK. Highly reliable with strong engineer support. 12-year warranty available on some models.
Vaillant
£700-£1,300
German engineering, quiet operation, and good efficiency ratings. A favourite among installers and consistently well-reviewed.
Viessmann
£800-£1,400
Highly efficient and very quiet. Often described as the premium choice. Strong long-term performance and low running costs.
Ideal
£600-£1,000
Budget-friendly with decent reliability. Good choice if cost is the priority. Made in the UK. Parts are widely available.
Baxi
£650-£1,100
Good value mid-range. British brand with a long track record. Spare parts are easy to source. Popular choice for rental properties.
Brand vs installer matters
A good boiler fitted badly will fail sooner than a budget boiler fitted well. Choose a Gas Safe registered engineer with strong reviews as much as you choose the boiler brand.
Is a Combi Right for You?
Combis heat water on demand with no separate hot water cylinder or cold water tank. That saves space but has limits.
Good fit if:
- +You have 1 or 2 bathrooms with moderate hot water use
- +You want to free up space by removing a hot water cylinder or loft tank
- +You have good mains water pressure
- +The household uses hot water one shower or tap at a time
Not ideal if:
- -You have 3 or more bathrooms (simultaneous use drops pressure)
- -Multiple showers running at the same time is common in your home
- -You have a large existing hot water cylinder you want to keep
- -Mains water pressure is low in your area
If a combi is not suitable, consider a system boiler with a separate hot water cylinder. These typically cost £2,000 to £4,500 installed and handle higher demand well.
What Will Your Running Costs Be?
A new A-rated combi uses significantly less gas than a boiler from 10 or 15 years ago.
Average annual gas bill
£600-£1,000
Typical 3-bed house with a combi
Saving vs old boiler (15+ yrs)
£200-£400/yr
Moving from 78% to 94% efficiency
Smart thermostat saving
£100-£200/yr
Nest, Hive, or Tado connected control
Payback period
If your old boiler is over 15 years old and runs at around 78% efficiency, replacing it with a modern 94% A-rated combi could save £200 to £400 per year on gas. At that rate, a £2,500 installation pays itself back in 6 to 10 years, and the boiler should last 12 to 15 years.
What Happens on Installation Day
Knowing what to expect makes the day straightforward. Most installs go smoothly when the engineer has full access and the gas meter is accessible.
Like-for-like swap
1 day
- New boiler fits in the same position
- No pipework rerouting needed
- Flue exits through existing hole
- Most common scenario
Relocation or conversion
2 days
- Moving the boiler to a new location
- Converting from a back boiler
- Switching from regular to combi type
- New flue position required
The installation process
- 1.Drain the central heating system
- 2.Remove the old boiler and disconnect gas, water, and flue
- 3.Fit the new boiler and connect gas supply, water flow, and return pipes
- 4.Install or reuse the flue and any new thermostatic controls
- 5.Commission the boiler, test all radiators and hot water
- 6.Walk you through the controls, warranty registration, and annual service requirements
The engineer must be Gas Safe registered. Ask to see their card before work starts. You should receive a Building Regulations Compliance Certificate (Benchmark) after installation.
Common Questions
Does the price include removing the old boiler?
Yes, in most cases. Most Gas Safe installers include old boiler removal and disposal in their quote. Confirm this when getting quotes. Removing a back boiler behind a fireplace may cost an extra £200 to £400 due to the additional labour involved.
How long does a combi boiler last?
Most combi boilers last 12 to 15 years with annual servicing. Some premium models run for 20 years. An annual service costs £60 to £120 and keeps the warranty valid. Skipping services shortens the lifespan and can void the warranty.
Is there any government help towards the cost?
The Boiler Upgrade Scheme does not cover gas combi boilers as it is aimed at heat pumps. However, if you are on certain means-tested benefits, the ECO4 scheme may fund a full replacement for free. Check with your energy supplier or visit the government ECO4 page to see if you qualify.
Should I get more than one quote?
Always get at least three quotes. Prices for the same boiler can vary by £400 to £800 between installers. Use the Which? Trusted Traders finder or Checkatrade to find Gas Safe engineers in your area. The cheapest quote is not always the best; check reviews and ask what the warranty covers.
Combi Boiler Cost Calculator
Estimate your total cost based on brand, size, and installation type.
Estimated Total (supplied and fitted)
£1,700 - £2,900
Midpoint: £2,300
Breakdown
Warranty: 10 years (requires annual service)
Always get 3 quotes from Gas Safe registered engineers. Prices are UK averages for 2026.