The circulating pump is the heart of the heating system. It’s job is to circulate the hot water from the boiler around the pipework circuits to each radiator.
Theoretically it should be sized correctly to the system. In general there are two sizes used for most domestic house sizes (2-5 bedroom properties). They are either a 5metre or 6metre head pump.
They usually have a 3 speed adjuster used to vary the output over a set range.
As a guide it is best to set the pump on the lowest setting, if one or two radiators toward the end of the circuit do not heat up then you simply increase the speed setting to the next level until they do heat up.
It is now possible to obtain low energy electronic pumps which are able to vary their performance in line with the requirement of the heating system. These are particularly suited to system with thermostatic valves fitted to all the radiators.