How does Central Heating Work?

Most modern central heating systems in the UK have a boiler, radiators,
and heating controls including thermostats, programmers and motorized valves.
There may also be a hot water cylinder (hot water tank)
but this is not needed if there is a combination boiler (a combi).

There are a number of different types of central heating system.
Most modern systems are fully pumped but older systems use gravity
to heat the hot water and only used a pump for the radiators.

All central heating systems lose water over time and so there needs to be a way
of adding extra water to keep the heating system topped up.
When the water in the heating system gets hot it expands and has a bigger volume
(it takes up more space). All central heating systems need a way to accommodate
the extra volume when the water is hot.
The way that the central heating system deals with these two needs
depends on whether it is sealed or open vented.

Central heating systems are usually very reliable but can go wrong.