How to Replace a Central Heating Pump - A DIY Guide to Replacing a Central Heating Pump

Summary: Step by step guide on how to replace a Central Heating pump, and how to make sure it is working effectively. A faulty central heating pump can cause Central Heating faults. In this project you will learn how to disconnect the electrical supply to your pump and ensure you know where each wire goes when you come to reconnect it, what tools you should use to disconnect your old pump, how to turn off the inlet and outlet water supply to the pump and how to inset your new pump and reconnect the inlet and outlets and also the wiring. Once your new pump is in position we will also show you how to test the pump and bleed any air out of the system.

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Replacing a central heating pump can sometimes be a little awkward because of its position in the airing cupboard or similar.

The basic rules however remain the same and if you are struggling with an old spanner which does not fit properly, please use the correct tools for the job. It really does make life so much easier.

Adjustable spanner

Adjustable spanner for removing and refitting central heating water pumps

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Tools Needed for Changing Central Heating Pumps

To change a central heating pump you will need a couple of large adjustable spanners (Stilsons are probably the best type of wrench to use here, but if you can't get the stilsons in, see our project on spanners and wrenches)

The heating pump pumps water around your radiators, from the boiler, keeping them supplied with hot water . A good indication that the central heating pump is playing up is if your radiators are hot at the top of the house, but cold downstairs. Also, see our project on Central Heating Problems for more on faults within the Central Heating System. If this is the case it can sometimes be overcome by turning the pressure up on the pump.

Stilsons are easiest to use for replacing central heating pumps

A Stilson wrench is one of the best tools for removing and refitting central heating pumps

The heating pump is powered by electricity. This must be turned off and disconnected from the pump before you can change it. You must also turn off the central heating.

Buy the Correct Replacement Central Heating Pump

Before you buy a new pump, look at all of the labels and writing on the old pump. Many of these will contain pump specifications (speed of pump, flow rate etc) and will make it much easier for you to buy the correct replacement.

Also (having made sure the electricity is off) take off the electrical cover and take a digital photograph (you can even use your phone) of the connections inside.

If you cannot take a photo, make a diagram of the connections. This will help you put it all back together properly. It is much easier to have all of this information now than to struggle later.

Before you go ahead and purchase your new pump it's also a good idea to thin about what replacement pump you are going to buy. As mentioned above you will have to make sure that your new pump is up to the job of pumping water around your system and the existing pump should give you a good idea of the specs that you should go for.

Also it's a good idea to go for a modern energy efficient pump that will not only stand you in good stead for the future but also go some way to saving you money on your heating bills.

In terms of manufacturer, many heating engineers and professionals regard Grundfos as about the best you can buy but if you are in any doubt pop down to your local plumbers merchant or contact a professional heating engineers for advice.

Central heating pump in position

Existing central heating pump in position with main features indicated

The image above shows a pump in position near the floor of the airing cupboard.

Fully explained  and labeled central heating pump

A modern replacement central heating pump indicating all major elements

Removing and Replacing a Central Heating Pump

Disconnect Electrical Wires

Remove the electrical connection cover and release the wires from the live, neutral and earth positions (again, ensure the power is turned off!). Unclamp the cable from the connection box and pull it clear of the pump.

Turn off Inlet and Outlet Valves

The inlet and outlet valves need to be turned off using an adjustable spanner. These valves will turn off by turning them clockwise. If you have trouble with a valve that is stuck or jammed, view our project on this here.

Disconnect the Old Pump and Remove

Undo the nuts connecting the pump to the pipework using the Stilsons. Do not disturb the connection between the other side of the valves and the pipework.

There will be some water in the pump. You can either place some rags under the pump or a shallow paint roller tray to catch the drips. Keep the washers if you have to but it is best to replace these too. Once disconnected completely, remove the old pump.

Insert new Pump and Connect up

Place the new pump in position. Make sure that you have replaced the washers and ideally replaced them with new ones. (don't forget the washers) and tighten the connection nuts.

When a washer has been compressed for a long period of time, indents can be created in it's surface and it can also degrade over time, loosing some of it's flexibility and in most cases creating very small fracture lines or cracks when bent, so it's always better to replace any washers as you don't want to put it all back together and find it leaks due to simply not replacing a few washers.

Once in position and the washers are in place, tighten the connection nuts on the inlet and outlet. It's best to do this by hand until finger tight so that you can feel that the nuts have screwed on to the threads correctly and have not cross-threaded. Once finger tight you can then tighten with a wrench.

Again, don't over-tighten with the wrench as this may damage the threads.

Re-Connect the Electrical Connections

Remove the electrical connection box cover and use a light cloth to make sure no water is present. Reconnect the cable wires as shown on your photo or diagram.

Test the New Pump

Turn up the room thermostat (to get the pump working as quickly as possible) and reinstate the electrical power to the pump.

Once all of the elements of the pump have been connected up you can go ahead and turn on the central heating. Depending on the type and nature of the pump you have used you should be able to hear it kick in when it starts to pump.

Bleed any Air out of the System

There may be air in the system after changing the pump and you have created quite a bit of disturbance. As you can see in the image above, each pump will feature a bleed screw that will allow you to get any air out of the pump and the system. Open the screw very gently (normally by turning it anti-clockwise) until you hear a hissing. There is always the chance that a little water will escape at this point so it's a good idea to put some rags or a shallow tray down to catch any spillage.

It may also be necessary to bleed the radiators at this point as air may have been pumped some way round the system. For help on doing this see our bleeding radiators project.

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