There are three main types of high efficiency condensing boilers: the combination or 'combi', the system or the heat only boiler.  Please find a summary of each of these types below.

Combination (or combi) boilers

This type of boiler is the most popular and heats water instantaneously on opening the hot water tap.  There is no need for a loft tank or storage cylinder.  The water is fed from the mains so the water pressure is generally greater.  Because they provide hot water when you need it, combi boilers are also economical to run.

System boilers

These are designed to generate heat for your home as well as hot water that can be stored in a separate hot water storage cylinder.  This can be situated anywhere in your home with no need for a separate tank in the loft. 

Heat only boilers

These work in conjunction with a hot water storage cylinder and cold water top up tanks to provide a home with both central heating and hot water.

High efficiency condensing boilers

Government legislation states only high efficiency boilers can be installed in England and Wales except under special circumstances.  High efficiency condensing boilers recover as much as possible of the waste heat that would normally be rejected into the atmosphere from the flue of a non-condensing boiler, using one or possibly two heat exchangers.  Current legislation states that high efficiency condensing boilers must run at 90% efficient or better.

The type of boiler you need will depend on a number of factors, such as the size of your house and your hot water requirements.