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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Is a combination condensing boiler more efficient than a regular condensing boiler?
A combination (Combi) condensing boiler can be more efficient than a standard condensing boiler because it heats water as you need it. Combi boilers are most suitable for smaller homes, as they can only keep up with a certain level of demand. Non-combi boilers produce hot water and then store it in a cylinder for use as and when. This is still quite an efficient process - but if the hot water is not used immediately, then inevitably some heat will be wasted. It will generally depend on the size and amount of hot water you're likely to need. You installer will be able to advise you which type of boiler best suits your needs.
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.
How reliable are condensing boilers?
Condensing boilers are reliable if well maintained and serviced regularly. A Which? survey in 2011 found that 46% of owners who bought a boiler after April 2005 have experienced some kind of fault. Not all of these faults required a repair. In fact the most frequent problem, a blocked drainage pipe, experienced by 11% of owners, is actually a problem caused by poor installation.
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