A “combi” or combination boiler heats both the water pumped round to heat your home and the hot water that comes out of your taps.

It heats water very quickly and efficiently so that there is no need to have a hot water tank.  Turn on a hot tap and in a matter of seconds you have running hot water – and enough of it for a bath or shower.

Moreover, the next person who wants a bath or shower can have one as soon as the last person has finished running the hot water without worrying about waiting for a hot tank to refill or reheat.  However, more than one person wanting to run a bath or shower at the same time is more of a problem; there is a limit to how much hot water the boiler can produce at one time.

A combi boiler may be more expensive to buy and install, but is cost-effective and energy-efficient to run since hot water is only produced when needed.

Alternatives to combi boilers are system or traditional boilers.  These types of boilers provide the hot water that circulates to heat your radiators and/or underfloor heating in the same way as combi boilers.

However, system or traditional boilers do not provide instant hot water.  Instead they work with hot water tanks, heating them.  It takes time to heat up a water tank, so once it is empty you have to wait for some time for more hot water.  On the other hand, when it is full it can provide hot water to several baths, showers or taps at the same time.

For more information on different types of boilers see our page explaining wet heating systems.