If you are unsure what boiler you currently have or what boiler you would like to be installed this brief guide will help you understand the common systems available.

Combination boiler

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A combination boiler (combi) provides heating and hot water directly from the boiler.

Here’s an example of a central heating and hot water system layout using a combi boiler:

A combi boiler is an ingenious space-saving idea, and an increasingly popular choice in UK homes. In fact, combis now account for well over half of all the new domestic boilers installed in Britain every year.

A combi boiler is both a high-efficiency water heater and a central heating boiler, combined (hence the name) within one compact unit. Therefore, no separate hot water cylinder is required, saving space within your home.

Further benefits of a combi boiler are significant savings 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 benefit of combi boilers is that it can generally save you money on installation time and costs, since no tank in the roof space means less pipe work and a shorter installation time.

Regular Boiler

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Regular boilers heat your central heating system directly and produce hot water for your cylinder.
Here’s an example of a central heating and hot water system layout using a regular boiler:

If you are replacing an older model of boiler, the chances are that you will have a regular (also known as ‘conventional’) boiler.

A typical regular boiler system incorporates a boiler, extended controls, a hot water cylinder, which is often fed by a cold water storage cistern located in the loft, and a feed and expansion cistern – also located in the loft.

System Boiler

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A system boiler heats your central heating system directly and produces hot water for your cylinder.
Here’s an example of a central heating and hot water system layout using a system boiler with an open-vented hot water cylinder:

An example of a central heating and hot water system layout using a system boiler with a pressurised unvented hot water cylinder:

A system boiler, just like a regular (conventional) boiler works on the principle of stored hot water. However, a system boiler differs from a regular boiler in some important respects.

Firstly, many of the major individual components of the heating and hot water system are built into a system boiler, which means that installation is quicker, neater, easier and more efficient.

Secondly, the hot water is pumped from the system boiler through the heating system to the radiators and hot water cylinder, resulting in a fast response and more economical running costs. The system boiler removes the need for a feed and expansion cistern.