Nearly all UK homes will use a central heating pump that is really the heart of the central heating system. Its funstion is to pump the heated water from the boiler, around the heating systems, radiators, hot water coil or both and then return to the boiler to be re-heated. Should a vital component like the pump fail, then all the services that you need will cease. It is therefore imperative to identify a fault, so it is a good idea to call a professional service like East London Plumbers. If the pump has failed, then a new one is required. Before you remove an old pump unit, make sure you know which way the flow i.e. which end the water comes in and which ended flows out, and the user marker pen to label it accordingly. These central heating pumps only rotate in one direction and have a flow arrow marked on the casing to help when the pump is being installed or replaced. Under the lead on the control box there is a screw connector where the electrical power is connected and fed from the central heating control. There could also be a dial or screw which is fitted so that the pump speed can be adjusted manually by you. An East London Plumber can supply and fit new heating parts. The motor when running normally should make almost no discernible noise, although if you put your hand on it, you should be able to feel a slight vibration, which is normal. The large screw situated on top of the pump is almost definately the bleed screw and is fitted to allow the homeowner or a professional plumber to purge any air that may be inside. No central heating pump is able to prime itself, therefore if air was to leak in, the pump would not be able to get rid of the air until it is bled out manually. This can be done by loosening the screw slightly until the hissing sound stops and then tightening the screw back up again.