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. Before you remove an old unit, make sure you know which way the flow is, with gender water comes in and which ended flows out, and the user marker pen to label it accordingly. An Edgeware Plumber can fit a pump.Under the lead on the control box there is a screw connector with electrical power is connected and fed from the central heating control. There may also be a dial or screw which is fitted so that the pump speed can be adjusted manually. On some units, you will notice that a metal or plastic cylinder about the size of a salt cellar is fitted onto the pump. This is called a smoothing capacitor and this prevents the pump motor from causing any interference to any of the domestic electrical equipment fitted within the home such as a television and radio. This item cannot be replaced. Edgeware Plumber fit new central heating pumps. 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 totally normal. A large screw situated on top of the pump is almost certainly the bleed screw which is fitted to allow the homeowner or a professional plumber to release any air that may be in the pump. Central heating pumps are unable to prime themselves, 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 is done by opening the screw slightly until the hissing sound stops and then we tightening the screw.