Replacing your boiler

Boilers account for around 55 per cent of what you spend in a year on energy bills, so an efficient boiler makes a big difference.

Replacing an old gas boiler with an A-rated high-efficiency condensing boiler and improving your heating controls will significantly cut your home's carbon dioxide emissions - and could save you as much as £305 a year.

How much could you save?

Why are new boilers more efficient?

Installing a new boiler

Finding an installer

Other products


  How much could you save each year?

This will depend on how old and inefficient your existing boiler is.

Old boiler rating

Semi detached house

Detached house

Detached bungalow

Mid terrace house

Mid floor flat

G ( < 70%) £305 £490 £275 £250 £130
F (70–74%) £230  £365 £205 £185 £95
E (74–78%) £190 £310 £170 £155 £75
D (78–82%) £160 £255 £140 £130 £60

These are estimated figures based on installing a new A-rated condensing boiler and full set of heating controls in a gas-heated home.  Savings will vary depending on the size and thermal performance of your home

 The costs for replacing a boiler will vary, but a straightforward gas boiler replacement will typically cost around £2,300.


  Why are new boilers more efficient?

Modern boilers are more efficient for several reasons, but their main advantage is that they are all condensing boilers. All well-maintained boilers burn their fuel very efficiently, but they inevitably lose some heat in the hot gases that escape up the flue. A condensing boiler has a bigger heat exchanger, so it recovers more heat, sends cooler gases up the flue and is more efficient.

Sometimes the flue gases get so cool that the water vapour in the gas condenses out (hence the name). When this happens, even more energy is recovered from the condensing vapour, and the efficiency gets higher still.


  Installing a new boiler

If it is time to change your boiler, then the first thing is to decide what type of boiler you need.


The right fuel

If you have mains gas, then a gas boiler is usually the cheapest heating system for you.

If you don’t have a gas supply to your home, it might be worth looking into getting a gas connection. If there is no gas pipe near your home then this may not be an option, but if it's available just round the corner then it might be worth paying for a new connection. The company that owns and operates the gas network in your area may be able to help with the cost of getting a new connection, and it may even be fully funded.

To discuss a new gas connection, and to find out if you can obtain help towards all or part of the cost, contact the company that owns the gas network in your area.


The right boiler

Most old gas and oil boilers are regular boilers - they have a separate hot water cylinder to store hot water, rather than providing it directly from the boiler. When you replace your boiler you have a choice of buying a new regular boiler, and keeping your hot water cylinder, or buying a combi boiler that doesn't need a cylinder.

A regular boiler is more efficient than a combi at producing hot water in the first place, but then some heat is lost from the hot water cylinder, so a combi may be more efficient overall. The best option for you will depend on a number of factors:

  • How much hot water do you use? A large family using lots of hot water could be better off with a regular boiler – a smaller household using less may be better off with a combi.
  • Are you short of space? A combi boiler doesn’t need a hot water cylinder, and so needs less space.
  • Are you thinking of installing solar water heating? Many combis are not compatible with solar water heating or cannot use it so effectively.

  Finding an installer

For a list of registered installers go to the competent person website, SNIPEF, or

For gas and LPG boilers, the installer must be Gas Safe registered. For oil boilers we would recommend that you use an OFTEC registered installer. You can find registered installers at and

It’s worth getting three quotations from installers. You may also want to check that installers:

  • have a local office
  • have been in business locally for several years
  • have customer references that you can check.

The Heating and Hotwater industry Council website at also has advice and information, including a useful list of what should be included on a quote, and everything you should be told after your new boiler is fitted.

Your registered installer will ensure that your system complies with Building Regulations, and will make sure you get all the documentation to prove this. Keep these documents safe – you will need them when you sell the property.


Other products  


Heat recovery devices and systems

Heat recovery systems can save up to 17% of the energy used in heating your water. Some of the heat generated by your boiler escapes through the flue. Passive flue gas heat recovery systems capture some of this lost energy and use it to heat your water, making your heating system more efficient and saving money.


Hot water cylinders

New hot water cylinders are factory insulated to help keep your hot water at the right temperature for longer. They play an important role in supplying you with readily available hot water, so it’s important that they are fully insulated to prevent heat escaping.

Upgrading your hot water cylinder to a new one can save you around £20 to £30 a year.