How to bleed a radiator

This is a quick guide for those people not familiar with bleeding their own radiators

Radiators can stop working properly when air gets trapped at the top making this part of the radiator cooler than the rest. The more air collects, the colder it gets.

To get the air out you need to open the bleed valve. Bleed valves can be in various postions on the radiator, but they are all at the top somewhere. Some might be hidden behind a plastic cap. Double radiators might have one on each panel. They can be recognised by their distinctive square shape.

You will need a radiator key to open the valve. They come in various shapes and sizes, but they all have the same end fitting.

Before starting, protect the wall and carpet with old towels!

Then turn off the central heating

Use a paper towel under the key to catch any splashes. Undo the bleed valve by turning it anti-clockwise. It can be tight so you might have to use some force. You should only need to turn it one turn and you should hear the air coming out. Don’t unscrew it fully.

You will hear it starting to hiss. Be prepared for the water to come out in a jet – when the water appears, tighten it back up.

If you have a combination boiler or pressurised heating system, you may have to repressurise, expecially if you are bleeding a big radiator.

The pressure will drop as you release the air. If it falls to zero you will have to retighten the bleed insert, go and pressurise the system and then continue with the bleeding.

Another problem you might have is that the air vent becomes blocked from the inside. This shows itself when you undo the vent and no air comes out.

What you need to do now is close off both radiator valves.

Remove the bleed insert.

And clear the blockage with something thin and rigged like a needle or wire.

And clear the blockage with something thin and rigged like a needle or wire.

The air will probably rush out, but because you’ve turned off both valves, little or no water should come out. Now replace the bleed insert, open the radiator valves and bleed the radiator as before.

Now switch the heating back on. All done!