How to change your central heating pump

When the time comes to replace your central heating pump, we've got an easy-to-follow guide to installing a new device.


You can do without first draining down the whole central heating system, provided there are service valves fitted on each side of the pump.

What you'll need
  • Electrician's screwdriver
  • Bowl
  • Towels
  • Pipe wrench or adjustable spanner
  • Pencil and paper
  • New pump
Before you start

Domestic pumps are now a standard size, but if the old pump was longer than the new one, you may need adapters to fill the gaps.

When you go to buy a replacement from a plumbers' merchant, take all the details and measurements of the old pump with you. Also, make a note of the type of pump and the setting of its output regulator.

Simple steps

1. Switch off the electricity supply to the central heating system controls at the consumer unit.

2. Make a note and sketch of how the electrical wiring on the old pump is connected. It may be helpful to label each wire. Then disconnect the wires with a screwdriver.

central heating pump

3. Close down the service valves on each side of the pump using the valve handle or an adjustable spanner. If there are no isolating valves, drain down the system.

4. Put a bowl and towels under the pump ready to catch any water that escapes when you remove it.

unscrew pump

5. Unscrew the union nuts holding the pump in place. Turn them counter-clockwise (facing along the pipe towards the pump). Remove the old pump.

new pump

6. Fit the new pump in position with the new sealing washers in the unions to prevent leaks.

7. Open the isolating valves (or refill the system) and check that the unions are watertight.

checking new pump

8. Dry the pump carefully to remove any traces of moisture; reconnect the wiring.

9. Test the pump by switching on the electricity supply and turning on the central heating system at the programmer or time switch. You may also need to turn up the room thermostat to get the system going.

10. Once the central heating system has started up, check that the open safety-vent pipe over the feed-and-expansion cistern doesn't discharge water when the pump starts or stops. If it does discharge water, seek expert advice.

11. If you've had to add lots of fresh water to the cistern, bleed any air out of the system in order to guard against future corrosion and to protect the new pump.