How to Change a Central Heating Pump

Before you begin we recommend watching this quick instructional video then read on for more detailed advice:

Most houses have a central heating pump which acts as the ‘Heart’ in your heating system. It circulates heated water out of the boiler, round the system (radiators, hot water coil or both) and back to the boiler for re-heating.

If this vital component fails then you will receive none of these services. It is therefore imperative to know how to identify the fault and remedy it. Screwfix sell a wide range of central heating pump at a competitive price.

How do I know my heating pump has failed?

1. Are your radiators or hot water coil receiving hot water? You can feel the pump body to see if it is hot or the pipes going to the water coil, radiators or diverting valve.

Tip: If it is only luke warm after 10 minutes then it might be receiving a slight amount of heat by convection.

2. Can you hear the pump running? The best way to do this is to use a large flat bladed screwdriver. Press the flat blade on the end of the pump body and then press your ear on the handle of the screwdriver. You should hear the whirring of the pump.

Tip: Sometimes the pump might be running and circulating water but making lots of noise. This usually means the bearings have got water in them or the impellor is damaged. It can also mean air is trapped in the pump.

3. If the pump has a bleed screw can you see the pump shaft rotating? Remove the screw and look at the shaft. They usually have a flat bladed insert to test if the pump is seized. If the pump is in a dark airing cupboard, lightly insert a small screwdriver into the pump shaft. You should feel the screwdriver shake and maybe spin.

4. Is the pump receiving an electrical supply? Ask a qualified electrician to test the connections on the pump to identify if there is a supply.

If you are getting none of the above then your pump has failed and you will need to change it.

Why buy my own central heating pump?

You can buy many types of central heating pump online. If you buy he pump yourself you avoid an engineers mark-up thus saving money. If you aren’t sure which pump to buy ask your installing engineer. He should tell you.


Changing the pump:

1. Turn all components off electrically. This means boiler, pump and any zone valves.
2. Shut the pump valves situated above and below the pump. Most valves turn clockwise to close.
3. Get a small bucket and open the screw on the end of the pump or one of the nuts holding the pump to the valve. If water keeps leaking out for more than a few minutes then the pump valves are not holding and you will need to follow steps 4, 5 and 6.
4. Turn off the water supply. This could be at the main or in your loft.
5. Identify any zone valves and set them to manually open (usually an arm on the side of the valve body)
6. Find the lowest drain point in the heating system and using a hose, drain the system of water.
7. Repeat step 3.
8. Once you have no water coming out, test the electrical connections and make sure they are dead. Remove the electrical connections making a note of live, neutral and earth.
9. Unwind the nuts that connect the pump to the valves and remove the pump. Check that the old seals have come off the valves: most new pumps are supplied with new seals.
10. If you have drained the system completely of water because the pump valves wouldn’t hold, replace those valves.
11. Fit the new pump in making sure the pump seals supplied with the pump are in place and that the connecting nuts to the valves are tight.
12. Open the pump valves. Shut the drain point and re-fill the system.
13. Test for leaks. If there are any leaks you may need to tighten up one of the joints or use some jointing paste.
14. If you have no leaks, drain the system again and re-fill with a suitable inhibitor (Sentinel x100 or Fernox).
15. Only now do you re attach the electrical connections in the right place and fit the cover back on the pump.
16. Turn on the electrics and test operation of the new pump.
Tip: Sometimes after draining down a heating system you can get air locks. Even if the pump is running fine you might not get a full flow to all radiators. The best thing to do in this situation is turn the pump on and off. This moves the water and air suddenly. You should be able to hear air gurgle its way around and eventually to the air vents. If you still have trouble with one particular radiator not getting hot you may have to consider ‘back filling’ which we also explain.

A List of household pumps:

Grundfos: UPS 15-50, UPS 15-60, Alpha+15-50, Alpha+ 15-60, Alpha2 15-50, Alpha2 15-60, Alpha pro 15-50, Alpha Pro 15-60

Wilo: Gold 50, Gold 60, Wilo smart automatic domestic circulator