A combi boiler provides heating and hot water directly from the boiler. A combi (or combination) 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, offering space saving within the property. Further benefits of a combi boiler includes hot water being delivered through your taps or shower at mains pressure. So you can enjoy powerful showering* without the need for a pump. Another combi boiler benefit 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 boilers (also known as ‘conventional’ boilers) heat your central heating system directly and produce hot water for your cylinder. 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.
A system boiler heats your central heating system directly and produces hot water for your 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.
The term ‘condensing boiler’ refers to the fact that the boilers produce condense from time to time. Condensing boilers use heat from exhaust gases that would normally be released into the atmosphere through the flue. To use this latent heat, the water vapour from the exhaust gas is turned into liquid condensate. In order to make the most of the latent heat within the condensate, condensing boilers use a larger heat exchanger, or sometimes a secondary heat exchanger. Due to this process, a condensing boiler is able to extract more heat from the fuel it uses than a standard efficiency boiler. It also means that less heat is lost through the flue gases.

Boiler efficiency

The official rating for boiler efficiency is the ‘SEDBUK’ scale. SEDBUK stands for ‘Seasonal Efficiency of a Domestic Boiler in the UK’.

What is SEDBUK

The SEDBUK rating was developed under the UK Government’s ‘energy efficiency best practice programme’ with the co-operation of boiler manufacturers, including Worcester. It provides a basis for fair comparison of different models of boilers. The SEDBUK rating is the average annual efficiency achieved in typical domestic situations. It takes into account sensible assumptions about climate, control, pattern of usage and other similar factors. The rating is calculated from laboratory tests together with other important factors such as boiler type, fuel used, ignition type, UK climate, boiler water content and typical domestic usage patterns. So, for estimating annual fuel running costs SEDBUK is a better guide than laboratory test results alone. The boiler’s performance is scored, enabling the boiler to be placed in a banding system using a scale from ‘A’ to ‘G’. ‘A’ rated boilers are the most efficient. SEDBUK was introduced in 1999 and has undergone a number of changes since then, the latest being from SEDBUK(2005) to SEDBUK(2009). Where boiler efficiency is quoted simply as ‘SEDBUK’ it should be assumed this refers to SEDBUK(2005).

Condensing boiler regulations

Building regulations that have come into force since 1st April 2005 state that any replacement or new gas or oil boiler must be a condensing boiler. Rare exceptions may apply.