Updated on: February 9, 2026

Infographic for blog: replacing a back boiler with a combi boiler

Replacing a Back Boiler with a Combi Boiler

Back boilers are still extremely common throughout the UK. Whilst they have been deemed illegal to install if there is no alternative heat source solution, there are still many heating homes. A lot of the time, back boilers remain installed despite their inefficiencies and are only replaced when they finally breakdown. Find out more about these old boilers and learn why you should remove back boiler and replace with a combi boiler even before your current back boiler breakdown.

What is a back boiler?

A back boiler is a heat source that is fitted behind a fireplace within the home. They are the heat source for the houses heating system and provide heat for both the water system and the heating. These boilers became very popular in the 1960s because they could easily be tidied away meaning they required less space. It was also a fact that they were considerably cheaper to install than regular boilers making them an attractive option.

Why are people changing a back boiler to Combi boilers?

Many households think about replacing a back boiler because of the inefficiency level. It has been proven that back boilers are under 80% efficient meaning anyone using a back boiler will be paying more for their energy and require more energy to heat the home. Not only this, back boilers require a separate water tank, whereas modern combi boilers are both the heat source and hot water combined in one. A combi produces instantaneous hot water similar to an electric shower.

Are back boilers dangerous?

Back boilers aren’t necessarily dangerous; however, they do produce more harmful toxins than other types of boilers such as the combi boiler. Back boilers tend to be dangerous even if they are not in use. Whilst people are replacing back boilers with combi boilers, it is an option to leave an empty boiler installed. Whilst this may save you on the upfront cost on the new boiler installation, it must be noted that old back boilers keep residual moisture which can have negative effects on your health. By installing a combi boiler and fully removing the back boiler these health risks can be avoided.
Is it easy to replace a back boiler with a combi boiler?
If you do choose to remove a back boiler and replace with combi boiler be aware that it is not a small job and tends to have a higher upfront cost than simply replacing a combi boiler with another combi boiler. Many opt to invest in their property when upgrading their system. It is important to be aware that a back boiler removal can result in structural changes where new pipework or a new fireplace may be needed which is why it does tend to cost more upfront. The great thing is, however, that once you install an efficient boiler you will start to enjoy lower gas bills making it worth the upfront cost.

Where will I install the combi boiler?

When changing to a combi boiler, it must be noted that you will need to house the combi boiler as these do not install behind the fire. Most homes will install them into the kitchen, airing cupboard where the water tank originally was or in alternative places such as a spare bedroom or in the garage. Whilst you will lose space, you will benefit from a more efficient system. Plus, more modern combi boilers are smaller than they were in the past so they will take up much less space than they once did.

If I Install a combi boiler into the airing cupboard how will I dry my clothes?

A big concern many have when having the option to install a combi boiler into an airing cupboard is where they can air / dry their clothes. This can be done on clothes horses/airers. If you do retain space in the airing cupboard, there is always the option to install a radiator in replacement of the hot water tank that was most likely installed in the space. There are a number of factors that need to be considered before proceeding with this but a reliable plumber will be able to identify whether this is a good idea.

What is the best combi boiler to install in replacement of a back boiler?

All combi boilers are efficient and will most certainly improve your energy efficiency compared to a back boiler. We can, however, say that if you install a Worcester Bosch boiler with us you will benefit from an extended guarantee which is a huge bonus when you consider how important your boiler truly is.