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How to bleed or vent a boiler pump?

How to vent or bleed a boiler pump?

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Why would you need to bleed a boiler pump?

Image of a water from a central heating system draining through a hosepipe If you replace your boiler pump or if you have to drain your central heating system for any reason, it is possible for air to get trapped in your boiler pump.
Image to illustrate a burned out pump (they don't actually go on fire) Running a pump that has air in it can cause it to become damaged and burn out. (Don’t worry – they don’t actually set on fire!)
Image of a DIYer bleeding a boiler pump This can be avoided by bleeding the air out of the pump. This process is also known as venting.

Bleeding a boiler pump

Image showing a DIYer turning off the electrical power supply at the fuse box

Step 1 – Turn off power

Turn off the power at the fuse box and make sure it cannot be accidentally reconnected.

Image of gate valves either side of a boiler pump

Step 2 – Protect against water damage

Use 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 – Remove bleed screw cover plate

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

Use the long, flat bit in the multitool’s handle to unscrew the bleed screw cover plate by twisting anti-clockwise.

Image showing water trickling out of a bleed screw cover plate on a boiler pump You will know that you have successfully bled the air out of your pump when water begins to trickle out when you turn the shaft.
Image of a young DIYer keenly mopping up some leakage from their boiler pump

Step 4 – Replace bleed screw cover plate

Replace the bleed screw cover plate and mop up any spillage.

Image of a DIYer reconnecting their power at the fuse box

Step 5 – Reconnect power

You can now reconnect the power and reactivate your pump.

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