Standard Central Heating System

A standard central heating system, which sends heated water from a boiler to radiators and to the hot water cylinder heating coil, has its own small feed and expansion cistern in the loft. This tops up any water losses due to leaks or evaporation and also provides room for the central heating water to expand as it heats up. The cistern is supplied by a branch pipe from the rising main, and fills via a float-operated valve in the same way as the main storage cistern. A second open vent pipe looping over the feed and expansion cistern provides an escape route for air or steam should the heating system overheat for any reason.