A central heating system has pipework and radiators which are connected to a boiler. The boiler provides the heat and the pump moves heated water from the boiler through the pipework to the radiators, and back to the boiler for reheating. It also provides hot water to the hot taps in your home.
There are generally two types of boiler:
A conventional boiler – this system has a pump, a programmer and a room thermostat. You can control the heating and hot water separately by using the programmer. It heats hot water and stores it in a cylinder, usually found in your airing cupboard.
A combination (combi) boiler – this system has a programmer and a thermostat. It only needs to control the heating, as it heats hot water on demand. Hot water is available whenever you turn on the hot water taps and so does not need a cylinder to store it in.