What is a Back Boiler?

Back Boilers (also known as back boiler units or BBUs) became popular in 1966 with the launch of the original Baxi Bermuda.


A back boiler is a small, compact boiler fitted at the back of an open fireplace hearth. It sits behind a gas fire and provides hot water and central heating to the property.


Back boilers were popular until the Building Regulations changed in 2005, when it became a requirement to install high efficiency condensing boilers. Although many have been replaced with wall-hung condensing boilers, there are still a large number of back boilers still installed in UK homes.


An old standard efficiency back boiler is less than 70% efficient – so for every £1 of gas burned, on 70p worth of useable heat is generated and the other 30p worth is lost up the chimney. By replacing it with a new boiler at over 90% efficient, fuel bills can be reduced by up to £305, according to the Energy Saving Trust.

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Related FAQs

What should my boiler pressure be set at?

Normal operating water pressure for your boiler & central heating system is between 1.0 and 2.0 bar. Find out how to troubleshoot when the pressure drops.

Why should I get the water in my central heating system cleaned?

If your boiler breaks down due to sludge in the system, the repair work is not covered under your warranty and can lead to expensive repair bills as a result.

How do I know if I've got sludge in my central heating system?

Issues with your radiator temperature, leaks from your boiler, and unusual sounds from within your system are all indicators that there is a buildup of sludge.

Should I turn off my boiler in the summer?

Generally, it is best to keep your boiler switched on even during the summer months, however this can depend on your home and your circumstances.

Is a condensing boiler a combi boiler? 

Is a condensing boiler the same as a combi boiler? The short answer is yes. However, there are 3 types of condensing boilers.

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