Below is the step by step method for the replacement of a Central heating pump:1). Isolate the electrical supply for the whole system either by removing the relevant fuse(s) or switching off the circuit breaker(s). Bounds Green Plumbers carry out all forms of plumbing work.2). Either make a sketch or take a clear photo of all the connections for the pump so that reconnection is made easy. Then disconnect the electrical connections on the pump.3). If there are isolating valves or shut off cocks on either side of the pump make sure they are isolated. If there is nothing then the system must be drained before the pump can be removed. To drain you will have to connect a hosepipe to the lowest point in the system and run out of the house and make sure that secure the inlet system i.e. ball cocks that allow the system to fill are locked off so no water can refill. If you are not confident then call a professional plumber like a Bounds Green Plumber who is qualified.4). Open the drain cock and allow the system to drain. Place towels (old) around the pump and with the correct size spanners or adjustable wrenches undo the large securing nuts, then lift the pump clear.5) Visually inspect the pump for the presence of debris inside that would stop the impeller from spinning, if there is a blockage then clear it out and replace the pump with new fibre washers.6). If you need to replace the pump with a new one (should the removal of debris not work), take the old pump to a supplier in order to get a perfect match for the new. Refit the new pump and reconnect as per the diagram or photo of connections.7). Close the draincock and place some corrosion inhibitor into the feed and expansion tank and refill the system. Bleed the air out of the pump and all the radiators and re start the system.