New boiler: what it costs and how to replace yours

A typical gas boiler replacement costs about £3,500, according to the Energy Saving Trust, and Which? puts installation anywhere from about £1,400 to £7,000. Below: whether it's time, which type and size, how to compare quotes, warranties and doing it legally. Every figure comes from the Energy Saving Trust, Which?, the Centre for Sustainable Energy, Gas Safe Register, the government or the manufacturers.

Repair or replace?

Most boilers last 10 to 15 years. Energy Saving Trust, Worcester Bosch, Baxi
Worcester Bosch says it may be time to upgrade if repairs become more frequent, parts get harder to find or the boiler gets noisier. Worcester Bosch
Which? doesn't recommend replacing a boiler before it's necessary, because heating systems are expensive to install. But if yours is unlikely to last the winter, having a plan ready saves a last-minute decision. Which?

Combi, system or regular?

Combi: heats water as you use it, with no tank. Which? says it's best suited to smaller homes with one bathroom, and the Energy Saving Trust says it may suit homes with several bathrooms less well. Which?, Energy Saving Trust
System: stores hot water in a cylinder. The Energy Saving Trust calls it a good choice for larger families with higher hot water needs. Energy Saving Trust, Which?
Regular (heat-only): uses a cylinder and tanks in the loft. The Energy Saving Trust says it tends to suit larger properties or low water pressure. Which? says the same about system boilers, so ask your installer which fits your water pressure. Energy Saving Trust, Which?

What size boiler do I need?The kW manufacturers recommend for your home Radiator size calculatorIf you're changing radiators too

What a new boiler costs

The Energy Saving Trust puts a typical gas boiler replacement at about £3,500 (replacing an old G-rated boiler with an A-rated one, with thermostatic radiator valves), or about £3,900 with a full set of heating controls. Energy Saving Trust
Which? says installation can typically cost anywhere from around £1,400 to £7,000. Which?
Changing type costs extra. Which? estimates £400–£800 more to switch from a system or regular boiler to a combi, and £350–£750 for a vented cylinder or £900–£1,400 for an unvented one if you go the other way. Which?
Other extras Which? lists: a power flush £300–£750 (about £500 on average), a smart thermostat £100–£250, and upgrading the gas supply pipe £100–£400. Moving the boiler adds to the cost too. Which?

Getting quotes

Get at least three quotes from different installers. The Energy Saving Trust and the Centre for Sustainable Energy both recommend it. Energy Saving Trust, Centre for Sustainable Energy
Check every installer is on the Gas Safe Register. The Centre for Sustainable Energy says it's illegal and potentially extremely dangerous for anyone not fully qualified to fit a boiler. The Energy Saving Trust also suggests looking for TrustMark installers. Centre for Sustainable Energy, Energy Saving Trust, Gas Safe Register
Compare like with like. The Centre for Sustainable Energy says the new boiler should be A-rated, fitted with a room thermostat and a programmer (or a programmable thermostat), and that the installer should flush the heating system. Check each quote says whether it includes these. Centre for Sustainable Energy
Ask how long the manufacturer's warranty will be with that installer, since some long warranties only come through accredited installers (see below). Vaillant, Worcester Bosch
Keep the paperwork. The Energy Saving Trust says you'll need the compliance documents when you sell your home. Energy Saving Trust

What you could save

The Centre for Sustainable Energy says upgrading a semi-detached home on mains gas from a G-rated to an A-rated boiler could save around £320 a year, at July 2026 energy prices. Centre for Sustainable Energy
The Energy Saving Trust says upgrading from a G-rated gas boiler with no heating controls to an A-rated boiler with full controls can save about £420 a year in Great Britain. Energy Saving Trust

Warranties: don't lose yours

Manufacturers offer long warranties on new boilers: up to 12 years on some Worcester Bosch and Ideal models, and up to 10 years on Vaillant's main ranges through their accredited installers. The length depends on the model and who fits it. Worcester Bosch, Ideal, Vaillant
To keep it, the boiler usually has to be registered within 30 days of installation and serviced every year. Vaillant and Ideal say an unregistered boiler drops to 12 months' cover. Worcester Bosch, Vaillant, Ideal

Getting it done properly

By law, the engineer installing a gas boiler must be on the Gas Safe Register. Check their Gas Safe ID card. Gas Safe Register
A Gas Safe engineer notifies your local authority for you (Building Regulations), and you get a certificate in the post. Ask for the completed commissioning paperwork, such as the Benchmark certificate. Gas Safe Register, gov.uk

Thinking about a heat pump?

In England and Wales, the Boiler Upgrade Scheme gives £7,500 towards an air source or ground source heat pump, installed by an MCS-certified installer, when it replaces fossil fuel or electric heating. Homes on oil or LPG without mains gas can get an extra £1,500 until March 2027. gov.uk, Ofgem
In Scotland, Home Energy Scotland offers a heat pump grant of up to £7,500, an optional interest-free loan of up to £7,500 more, and £1,500 extra for rural and island homes. Home Energy Scotland
Heat pumps run cooler than boilers, so radiators may need to be bigger. Our radiator size calculator allows for that. Stelrad

Get it checked first

If your boiler has stopped with a fault code, find out what it means before deciding. Many faults are cheap fixes. Look up your code.

Common questions

How much does a new boiler cost in the UK?

The Energy Saving Trust puts a typical gas boiler replacement at about £3,500, or about £3,900 with a full set of heating controls. Which? says installation can range from around £1,400 to £7,000 depending on the boiler and the work involved.

How many quotes should I get for a new boiler?

At least three, from Gas Safe registered installers. The Energy Saving Trust and the Centre for Sustainable Energy both recommend it. Check each quote includes an A-rated boiler, heating controls and a system flush.

How long should a boiler last?

Usually 10 to 15 years, according to the Energy Saving Trust, Worcester Bosch and Baxi. Baxi says annual servicing helps it reach that.

How much could a new boiler save me?

The Centre for Sustainable Energy puts it at around £320 a year for a semi-detached home moving from a G-rated to an A-rated gas boiler, at July 2026 prices. The Energy Saving Trust says replacing a G-rated boiler with no controls with an A-rated boiler and full controls can save about £420 a year in Great Britain.

Do I need to register my new boiler?

Yes, to keep the full warranty. Worcester Bosch, Vaillant and Ideal all require registration within 30 days, and annual servicing.

Sources

Last reviewed October 2026. Spotted something that doesn't match your manual? Email hello@boilercodes.co.uk and we'll check it. How we check