A good rule of thumb if you need to replace something like a pump from a system, firstly ensure that you identify any direction of flow for the pump and its pipework. Then assuming that you are going to replace it, make sure you have used the pumps details in order to purchase a new one. If you are taking it out for some other reason, then label all connections so that you can re-fit afterwards. An SW1 Plumber can fit a CH pump. Isolate the power to the central heating at the consumer unit to ensure the direct electrical feed to the pump is off. Isolate the spindle operated water valves either side of the pump C H pumps can only rotate in one direction and have a flow arrow marked on the casing to help when the pump is being installed or replaced. You can disconnect the electrical power on the pump by unscrewing the cover of the terminal box which is normally fitted on the side of the pump, checking with a tester that there is no voltage at the terminals. If you are not confident do not attempt this job. Call a professional service like SW1 Plumbers. There will also be a dial or screw which is fitted so that the pump speed can be adjusted manually. Once disconnected you can then undo the nuts on the pipe and remove the pump. Then carry out the work and replace as required.

NB: The motor normally runs quiet with no discernible noise, although you should be able to feel a slight vibration. The large screw situated on top of the pump is the bleed screw and is fitted to allow any air in the pump to be bled out. Central heating pumps cannot sef-prime, therefore if air was to leak in, the pump would not be able to get rid of the air until it is bled out at the screw. This is done by loosening the screw slightly until the hissing sound stops and then tightening the screw back up again.
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