Central heating pumps or circulating pumps, as they are also called, can be relatively easy to replace. Over time a heating pump can fail for various reasons including sludge build up in the system where the debris wears the pump impeller or, if the pump has been allowed to run dry.
Heating Pump Electrical Faults
Other common problems include electrical faults so you should test for this first before rushing to replace the pump. Isolate the electricity supply at the consumer unit before removing any covers to inspect the wiring. Check that any fuses protecting this circuit have not blown, and if necessary, replace. Check for loose connections where the wires connect to the terminals of the pump. Each wire should make good contact and be properly secured. If needs be, remove the wires, cut the ends cleanly and retrim the insulation to suit before reconnecting them.
Remove the Faulty Heating Pump
Isolate electrics at the consumer unit for the circuit supplying the power to the pump and switch off boiler. If the system is hot, allow to cool first. Either side of the pump there should be a valve allowing the water supply to be isolated. These should both be closed using a wrench to turn the square headed spindle. If there are no valves or they have seized, the system will need to be fully drained before proceeding. In this case you should also fit an isolation valve either side of the new pump allowing for ease of future maintenance.
Before undoing anything, make absolutely sure your new pump is the same size as the original so that it will fit without any adjustment to the existing pipe work. Check the direction of flow on the original pump – you will need to fit the new one the same way round. Disconnect the electrical supply to the pump by undoing the terminal housing and releasing the live neutral and earth conductors.
Have a bucket and a collecting device to hand – a simple plastic dustpan is very useful for this as it will fit snugly under the connections to collect water spillage even if the valves are quite tight to the wall. Start undoing first union nut on the flow side and you should only get a dribble of water which soon stops. A lot of water indicates that the valve is not closed. Hold the body of the pump with one hand while using a wrench to undo the nut. This should prevent the pump itself from turning, or loosening of the compression joint between valves and pipe work.
Repeat the process with the union nut on the other side of the pump and then remove the pump. Inspect the valves - they will probably need a bit of cleaning to remove debris and sludge. Remove the washer from each connection and replace with new ones.
Fitting a New Pump
Hold the new pump in position making certain it is the right way round. The direction of flow marked on the casing must be the same as it was before. Loosely connect the pump to the valves on either side by hand tightening the nuts. Be sure to line them up squarely so as to avoid cross threading which would damage the threads leading to leaks. Fully tighten the union nuts.
Open the isolating valve on the flow side first and check for leaks. All being well, you can now open the valve on the outlet side and again check for leaks.
Removing Air from the Pump
Bleed the pump by slackening the central screw head a little until water begins to dribble from it. Any air should be released. You may have to repeat this after the pump has been allowed to run for a while, but be sure to do this with the pump switched off.
Wiring the New Pump
Make sure everything in the area is perfectly dry before connect the electrical supply to the new pump. Open the terminal box on the new pump and wire the live neutral and earth to the appropriately marked terminals being sure to pass the flex through the protective grommet and any securing clamp. Replace the cover then switch the electrical supply back on at the consumer unit. Switch the boiler back on and turn on the heating. Make a further inspection of the valves to ensure there are no leaks.