Replacing my boiler

Heating accounts for about 60 per cent of what you spend in a year on energy bills, so an efficient boiler makes a big difference.

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 larger 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), and even more energy is recovered from the condensing vapour.

What should I consider when replacing my boiler?

If it is time to change your boiler, you need to decide what type of boiler is right for you. Here are some things to consider:

Fuel type

If you have mains gas, a gas boiler is likely to be the cheapest heating option. Based on average fuel prices at March 2016, oil is currently a cheaper heating fuel; however, historically oil heating has been more expensive.

If you don’t have a gas supply to your home, it might be worth considering a form of low carbon heating such as a heat pump or biomassWith the renewable heat incentive these may be a cheaper overall.

Alternatively you may want to get a gas connection to your home. 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. Contact them for further information.

Boiler type

Most old gas and oil boilers are regular boilers that have a separate hot water cylinder to store hot water, rather than providing it directly from the boiler. When you replace your boiler you can buy a new regular boiler, and keep your hot water cylinder, or buy 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.

Your hot water usage

Large families using lots of hot water are likely to be better off with a regular boiler, whereas smaller households using less may be better off with a combi boiler.

Space in your home

Combi boilers don’t need hot water cylinders, and so require less space in your home.

Compatibility with solar water heating

If you’re thinking of installing solar water heating, it’s worth noting that many combi boilers are not compatible with this heating system or cannot use it so effectively. 

Finding an installer

For a list of registered installers visit the Competent Persons RegisterSNIPEF, or HHIC.

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 on Gas Safe Register and OFTEC.

It’s worth getting three quotes from different installers, and 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 review.

Your registered installer will ensure that your system complies with current 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.

How much could I save each year?

This will depend on how old and inefficient your existing boiler is and the fuel your boiler uses. Below are some examples of potential savings for a home heated by gas central heating.

Upgrading an old gas boiler with a programmer and room thermostat, with a new A-rated condensing boiler with a programmer, room thermostat and thermostatic radiator controls (TRVs) could save you:

England, Scotland and Wales

Old boiler rating

Semi-detached house

Detached house

Detached bungalow

Mid terrace house

Mid floor flat

G ( < 70%)

£215

£350

£180

£175

£95

F (70–74%)

£145

£240

£125

£120

£65

E (74–78%)

£115

£190

£95

£95

£50

D (78–82%)

£85

£140

£70

£70

£35

These are estimated figures based on installing a new A-rated condensing boiler with a programmer, room thermostat and thermostatic radiator controls (TRVs) in a gas-heated home from an older boiler with a programmer and room thermostat. Savings will vary depending on the size and thermal performance of your home. Figures are based on fuel prices as of March 2016.

The costs for replacing a boiler will vary, but a straightforward gas boiler replacement plus thermostatic radiator valves will typically cost about £2,300 excluding radiators.

Northern Ireland

Old boiler rating

Semi-detached house

Detached house

Detached bungalow

Mid terrace house

Mid floor flat

G ( < 70%) £185 £285 £160 £155 £86
F (70–74%) £125 £200 £105 £105 £60
E (74–78%) £100 £155 £80 £80 £45
D (78–82%) £75 £120 £60 £60 £30

These are estimated figures based on installing a new A-rated condensing boiler and full set of heating controls in an oil-heated home. Savings will vary depending on the size and thermal performance of your home. Figures are based on fuel prices as of March 2016.

The costs for replacing a boiler will vary, but a straightforward oil boiler replacement plus thermostatic radiator values will typically cost about £3,000.

What else can I do to improve my central heating system?

Heat recovery devices and systems

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 you 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.

If you have an old cylinder you could save £25-£35 a year by topping up the insulation. Alternatively if you are replacing your cylinder, you can save energy by making sure that the cylinder is no bigger than you need it.

Chemical inhibitors

Corrosion deposits in an older central heating system can cause a substantial reduction in the effectiveness of the radiators, and the system as a whole. The build-up of scale in heating circuits and on boiler components can cause a reduction in efficiency too.

Using an effective chemical inhibitor can decrease the corrosion rate and prevent the build-up of sludge and scale, thus preventing deterioration and helping to maintain efficiency.