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How do you replace a boiler pump head?

Chris Chris
28th February 2020

How to replace a boiler pump head

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Image of the new boiler pump the DIYer has bought to replace their old one After checking for issues with your pump, you may have discovered a problem with your impellor, or there may be a problem with the pump’s electrics. Either way, if your pump isn’t working, you may find yourself needing to change it.
Image of a DIYer ready to remove the whole boiler pump from the central heating system using a pair of grips It’s possible to change the whole boiler pump but this guide specifically deals with removing the boiler pump head.

It’s unusual for there to be a problem with any other part of the boiler pump and this should be a quicker and easier way to solve your boiler problem.

What is a boiler pump head?
Image of a boiler pump head, clearly showing the impellor assembly A boiler pump head is the ‘business end’ of your boiler pump. It houses the impellor, which is the part of the pump that makes water flow around the central heating system. The rest of your pump assembly is really just an extension of your pipework.

Removing and replacing a boiler pump head
Image showing a DIYer turning off the electrical power supply at the fuse box

Step 1 – Turn off power

Make sure the power is switched off at the fuse box and cannot be accidentally reconnected.
Image of gate valves either side of a boiler pump

Step 2 – Protect against water damage

Turn the gate valves either side of your boiler pump to cut off the water supply using grips or pliers.
Image of a stack of towels ready to be laid down to prevent water damage to a DIYer's flooring Put down towels to protect flooring or electrics.
Image of a DIYer unscrewing the bleed screw cover plate on their circulator pump using a boiler pump multitool

Step 3 – Open bleed screw cover plate

Remove the bit that is currently in the multitool’s bit holder.

Use the flat bit mounted on the handle to unscrew the bleed screw cover plate, twisting anti-clockwise.
Image of water coming out of the bleed screw cover plate of a boiler pump

Step 4 – Check water

Any water that was in the pump head should leak out. This may be a trickle, or it may come a little faster depending on the problem that you’re experiencing with your pump.
Water dyed black by perishing rubber on the inside of a boiler pump If the water is black, or if it contains debris, you will need to drain your central heating system.
Image of a pipe in which sludge has been left to accumulate Keeping the water in your central heating system free of debris like this is important because it prevents the formation of sludge, which can make your radiators run cold at the bottom, or clog up your pump.
Image of an impellor that has become jammed due to debris circulating through the central heating system Leaving debris in the system could also damage the new pump head you are about to install.
Image of a boiler pump multitool fitter with an allen key bit

Step 5 – Remove pump head

Fit the correctly-sized allen key bit into your boiler pump multitool. Only one of the available allen key bits will fit into hexagonal indentations in the retaining screws so it should be easy to work out which is the right one.
Image of a DIYer using a boiler pump multitool to unscrew the retainer bolts on their circulator pump Unscrew all four of the screws holding the pump head in place.
Image of a DIYer detaching the boiler pump head from the rest of the boiler pump assembly Remove the pump head and set it aside. It may be wet and dirty, so avoid putting it on any surfaces that could stain.
Image of a DIYer removing a broken gasket

Step 6 – Check rubber gasket

Now that your boiler head has been removed, you can check the rubber gasket that sits in the part of the pump that attaches to the base of the motor that drives the impellor. If it is broken (like a snapped rubber band), pull it out and discard it.
Image of a DIYer placing a new rubber gasket into a boiler pump volute Replace it with a new rubber gasket. Make sure it fits snugly around the inside of the volute as this will create a seal and prevent leaks.
Image of a DIYer screwing in the retaining bolts on a new boiler pump head with a boiler pump multitool

Step 7 – Install new pump head

To fit a new pump head, all you need to do is line up the bolt holes and screw it onto the part of the pump assembly that’s still attached to the pipes.
Image of a gate valve attached to a boiler pump Switch the water back on. Leave the central heating system to refill if you drained it.
Image of a DIYer bleeding their boiler pump with the flat bit mounted in the head of a boiler key multitool You will now need to bleed your new pump. Follow the steps in the guide How to bleed or vent a boiler pump
Wonkee Donkee advises the DIYer to make sure that they bleed their pump to avoid damaging it
Image of a DIYer reconnecting their power at the fuse box Once your central heating system has been refilled and your pump has been bled, you can reconnect the power.
Image of someone who is too hot because they installed a new boiler pump and got carried away using their central heating now that it works again Your pump should now be working again, and suffering in cold rooms should be a thing of the past!

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