If you have a combination boiler, you have no need for a water pump, storage cylinder, feed and expansion cylinder, or any other separate components, and the fact that you don't need any of these bulky components can save you a considerable amount of space. And this is why the combi boiler is now the most common type used in Britain.

Combi boilers use essentially the same technology as standard boiler, but there are a number of functional differences between the two. All the water used in a heating system which uses a combination boiler is sealed in, negating the requirement for a feed and expansion cylinder. The combi boiler also has its own internal water storage cylinder, removing the need for a separate unit.

Rather than storing up hot water for tap use, a combi boiler heats water as it is required, with the hot water tap acting as a switch. Using its integral heat exchanger, the gas boiler can rapidly heat freshly drawn cold water by using an integral heat exchanger, which uses heat from the central heating system to heat the fresh water. This means that it usually only takes a matter of seconds after the hot tap has been turned on before hot water begins to flow from it.

Due to the fact that the boiler has to switch over to supply hot water to the taps, the central heating is turned off while the hot water is flowing. By turning off the hot tap, you are turning back on the central heating. A combination boiler can be a great choice for a smaller house or apartment, as it takes up far less space than its bulkier equivalents, but if you have more than two bathrooms, or need a lot of hot water for whatever reason, then you may have to go for a larger, multi component model.