In the last twenty years there have been two significant advances in domestic heating systems.

Firstly the change in water byelaws in 1989 allowed mains fed systems to be installed including combi boilers. With this change

came the introduction of sealed systems to domestic premises. A sealed system allows the heating water to circulate at greater pressure than an open vented (header tank) system, giving a more efficient distribution of heat around the home. Having no header tank also means that the system is not open to the atmosphere and is therefore unlikely to draw in air which in the past has caused circulation problems and hastened corrosion of radiators and sludge build up.

Secondly the introduction of condensing boilers (high efficiency) has made it possible to reduce heating bills and environmentally damaging heat losses.

Condensing boilers are now compulsory for most homes, and it is now even possible to get a high efficiency back boiler (installed behind a gas fire).   However it is sometimes possible to get an exemption if replacing an existing boiler would involve too many changes to pipework etc. Each case has to be individually assessed on a points system.

A condensing boiler extracts more heat from the flue gases before discharging them to the open air. This means that gas bills are lower for the amount of heat generated.

Because of these two changes there is now a variety of types of boiler in use:

Regular/ conventional boilers

heat a hot water cylinder and radiators. They are usually connected to an open vented

(header tank) system but may instead have a sealed system with its expansion vessel and other components fitted outside the boiler casing. They come in a variety of forms - floor standing, wall hung, back boilers etc.

A system boiler heats a hot water cylinder and radiators. It must be connected to a sealed heating system and the expansion vessel and other necessary components are contained within the boiler casing

A combi boiler is a combination of a system boiler with an instantaneous water heater. No

hot water cylinder is necessary, although in larger households it is possible to have a cylinder fitted in addition to the instant hot water, say for a remote bathroom.

All of these types can be high efficiency (condensing) or standard efficiency, but normally we now have to fit high efficiency boilers.

We normally recommend that mains fed systems are only fitted where the water main

provides adequate flow, especially if shared between flats.

A new type of boiler is now being developed which will provide "combined heat and power", generating electricity as well as heat for the home.