Costs, savings and maintenance

The current lifespan of condensing boilers is around 10-12 years, and though condensing boilers are reliable, you will need to get them serviced once a year.

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Costs for a new condensing boiler system do vary depending on how much work is required. Here is what you should expect to pay in some typical scenarios:

  • Replacing an existing gas condensing combination boiler in the same position. This involves removing and disposing of the previous boiler, then cleansing and flushing out the heating system before installing the new boiler. Expect to pay around £600
  • Replacing a gas non-condensing boiler with a condensing one in the same position. Extra plumbing, including a condensate drain will be needed, and cleansing and flushing out the heating system. Expect to pay around £750 – £850
  • Installing a new gas condensing boiler in a different location – this will involve upgrading your heating system by adding radiator valves and changing the controls. This involves more complex plumbing tasks such as adding a condensate drain and routing the flue. Expect to pay around £1,500 – £1,800
  • Swapping a gas heat-only boiler for a condensing combination boiler – The system will be converted from an open-vented setup to a sealed one. This will involve removing obsolete equipment, such as the hot water storage cylinder, cold water storage tank and the feed and expansion tank in the loft. Re-plumbing and adding a condensate drain will also increase the costs. Expect to pay around £2,000 –  £2,200
  • Replacing an electric heating system with a gas condensing boiler – This will involve connecting your house to the gas network, disposing of all your electric heating equipment and replacing the system with a boiler, radiators and heating controls. Expect to pay around £2,000 – £2,500
  • Replacing an electric heating system with an oil or LPG condensing boiler – This will involve disposing of all your electric heating equipment and replacing the system with a boiler, radiators and heating controls. Expect to pay around £2,500 – £3,000

(Source: Which)

It is often a good idea to change your boiler when you have other work done, such as fitting a new kitchen or bathroom, so as to reduce the cost and minimise disruption.


Because condensing boilers are very efficient, it is likely that installing one will save you money on your heating bills. How much you save will depend on your current heating system.

Condensing boiler savings

Replacing an electric system with a gas condensing boiler could save you over £500 a year on your bills.


Condensing boilers are fairly reliable; despite that, it is a good idea to ensure that you service your boiler annually. When your boiler is installed or serviced, your installer may need to clean and flush your central heating system, and possibly add a chemical inhibitor to help remove any limescale or sludge already in your heating system.

There are three main treatments which can be used:

  1. Flushing: This will either involve a `power-flush’, or a ‘mains pressure water flush’ to wash the system through.
  2. Inhibitors: Chemical inhibitors can be added to the system, helping prevent build up of lime scale and help prevent corrosion.
  3. Water softeners: water softeners can be added to the system in hard water areas.

Any maintenance work on your gas boiler should be carried out by a Gas Safe installer (previously known as CORGI). Oil boilers should be serviced by an OFTEC accredited installer.

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How can a condensing boiler save me money on my energy bills?
Condensing boilers are more efficient than standard boilers and therefore utilise less gas during operation. Modern conventional boilers can only offer a typical efficiency rate of 78%, whereas the rate for condensing boilers is around 88% - i.e. for every £1 spent spent on gas, 88p is converted to actual heat. This adds up to significant savings on annual gas bills, which will enable you to quickly recoup the initial outlay for the boiler and benefit from the extra savings. Complete our Home Energy Survey to find out just how long payback will take in your situation.
What does the Sedbuk efficiency rating mean?
Sedbuk stands for 'seasonal efficiency of a domestic boiler in the UK' and is now given as a percentage score. This score is an estimate of efficiency when the boiler is installed under typical conditions in Britain, taking into account climate, housing conditions, occupancy patterns, and controls.
How is the Sedbuk rating calculated?
The 'seasonal efficiency of a domestic boiler in the UK' (Sedbuk) rating for boilers is calculated from the results of standard laboratory tests, together with other important factors such as boiler type and the kind of fuel used. It describes the boiler's efficiency.
Could a condensing boiler save money on my energy bill?
Which? estimates that the average efficiency of boilers in UK homes is about 70%. This means they waste up to 30% of the heat they generate in the form of hot flue gases. This suggests that installing a condensing boiler, which has an efficiency of around 88%, can reasonably achieve savings of between £50 and £200 per year depending on the size of your house - and the saving will increase as the cost of gas increases. Complete our free assessment to find out just how much you could save.
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