What is a Combi (Combination) boiler?
The high efficiency condensing combination boiler is an ingenious space-saving idea. Combis are the majority of all the new domestic boilers installed in Britain every year.
The major difference between a combi and any other type of boiler is that a combi eliminates the need to store hot water — so no hot water cylinder in the airing cupboard. It is both a high-efficiency water heater and central heating boiler, combined (hence the name) within one compact unit which usually sits in the kitchen or utility room, or sometimes in the airing cupboard. The space savings result from the fact there is no hot water storage cylinder, cold water storage cistern or other familiar components of a regular (conventional) heating system.
The further benefits of this are a significant saving on hot water costs, and the fact that hot water is delivered through your taps or shower at mains pressure. So you can enjoy powerful showering* without the need for a pump. Another combi benefit is that it can generally save you money on installation time and costs — no tanks in the roof space means less pipe work and a shorter installation time.
A thermostatically-controlled shower safeguards against sudden changes in water temperature.
What is a regular boiler?
If you are replacing an older model of boiler, the chances are that you will have a regular (conventional) boiler. A typical conventional system incorporates a boiler and extended controls, a feed and expansion cistern, and a hot water cylinder (usually in the airing cupboard) which is often fed by a cold water storage cistern located in the loft.
What is a system boiler?
Unlike a combi, both a system boiler and a regular (conventional) boiler work on the principle of stored hot water — but a system boiler differs from a regular boiler in some important respects.
Many of the major individual components of the heating and hot water system are built in, which means that installation is quicker, neater, easier and more efficient.
The boiler includes an expansion vessel so there is no requirement for a feed and expansion tank in the loft, which allows the installation to save space.