The Energy Saving Trust Explain How You Can Save Over £340 A Year By Replacing Your Old Boiler.

Boilers account for about 55 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 usually the cheapest heating system.
If you don’t have a gas supply to your home, it might be worth looking into getting a gas 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. Contact them for further information.
Boiler type
Most old gas and oil boilers are regular boilers which use 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.
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.
1. Upgrading an old gas boiler without controls, with a new A-rated condensing boiler with a programmer, room thermostat and thermostatic radiator controls (TRVs) could save you:
England, Scotland and Wales

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 without controls. Savings will vary depending on the size and thermal performance of your home.

2. 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

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