Last updated on January 24th, 2024
A central heating pump is the beating heart of a central heating system which pumps the heated water around all the radiators and the hot water cylinder from the boiler.
If your pump stops working then your boiler and central heating system will stop working.
I have been fitting and fixing central heating systems for over a decade and have come across all sorts.
Here I’ll share what I’ve picked up over the years from my hands-on everyday experiences when replacing central heating pumps.
How to Replace a Central Heating Pump
Replacing a central heating pump is quite an easy job for a plumber. That is if the pump valves are working and they don’t start leaking when you close them for the first time in years.
If you’re replacing a pump for the first time, then it can be quite intimidating, especially if you haven’t done any type of plumbing before.
Here’s how to replace a central heating pump:
- Isolate the electrical supply to the heating system
- Trace the cable from the pump back to where it is connected and remove the 3 wires (unless it has a plug on the pump)
- Close the two pump valves on either side of the pump with a screwdriver or your hand or water pump pliers depending on which type of valves
- Put an old towel under the pump to catch any water
- Use some large water pump pliers or pump spanners to turn the two largest nuts on either side of the pump (this can be very difficult sometimes and you might need two people and some WD40)
- Remove the pump
- Refit the new pump in between the two pump valves with new washers and tighten up the two nuts
- Open the pump valves
- Bleed the pump using a large flathead screwdriver by turning the bleed screw in the centre of the pump anti-clockwise until some water comes out
- Connect the three cable wires to the same place where the old ones were
- Check for leaks and turn the power on then turn on the heating to make sure it’s working
Replacing Central Heating Pump Valves
Replacing the central heating pump isolation valves is a lot more complicated. If you are replacing the pump and you close the pump valves, more often than not the pump valves will leak because they haven’t been used for years or decades.
This means you will have to replace the pump valves.
You should make sure you use the same length valves as the ones you are replacing as there are a few different styles and sizes.
Here’s how to replace central heating pump isolation valves:
- Empty the heating system
- Isolate the electrical supply to the heating system
- Trace the cable from the pump back to where it is connected and remove the 3 wires
- Put an old towel under the pump to catch any water
- Use an adjustable spanner to undo the two smaller brass nuts on the pump valves that are touching the copper pipe
- You can leave the big nuts connected to the pump if you are replacing the pump as well
- Remove the pump and valves
- Connect the two new valves to the new pump using the new washers and tighten up the large nuts
- Place the pump and valves in place and tighten the nuts on each end
- Connect the three cable wires to the same place where the old ones were
- Refill the system
- Bleed the pump using a large flathead screwdriver by turning the bleed screw in the centre of the pump anti-clockwise until some water comes out
- Check for leaks and turn the power on then turn on the heating to make sure it’s working
How to Bleed Central Heating Pump
To bleed a central heating pump you need to unscrew the screw in the centre of the pump with a large flathead screwdriver.
You should turn the screw anti-clockwise and let the air out until water starts coming out.
Conclusion
Replacing a central heating pump is quite a difficult task if you haven’t done it before. Calling a heating engineer might be the best option if you haven’t done any kind of plumbing before.
There are quite a few problems that can arise when draining and refilling certain heating systems which can be a real headache even for experienced heating engineers.
If you have to replace the pump valves also, it might be best to leave it to the experts but if it’s just the pump and you feel competent, then go for it.
Feel free to ask me any questions in the comment section below and I’ll try my best to help.
Please share this post if you found it helpful.
FAQs
How long should a central heating pump last?
A central heating pump should last for decades. It really depends on your system and whether it’s dirty or overworking or constantly pumping air because of airlocks or other problems.
It’s also down to a bit of luck. Two-year-old pumps can fail.
You should be looking at a central heating pump lasting at least 10 years but maybe 20 or 30 or even 40 if you’re lucky.
I have removed pumps that are well over 40 years old and still working when changing a heating system to a combi boiler system.
Where is my central heating pump?
Your central heating pump will be inside the boiler on a combi boiler and system boiler.
If you have a conventional heat-only boiler then the central heating pump is usually next to the boiler or in the hot water cylinder (tank) cupboard.
If you are struggling to find the pump then it could be almost anywhere on your central heating system. I have found them under floorboards and behind walls in bathrooms.
Where is the bleed screw on a central heating pump?
The bleed screw on a central heating pump is in the centre of the pump. Usually a large circular piece of steel with a large crease across it for a screwdriver.
Do you have to drain the system to change the pump?
No, you do not have to drain the system to change the pump.
But, if the pump valves fail to hold the water when they are closed (or they start leaking) then you will have to drain the central heating system to change the pump and you will have to change the pump valves as well.
