Bleeding a Radiator

a radiator key
a radiator key
a bleed valve
a bleed valve

DO NOT bleed a radiator if you have a combination boiler. This type of boiler has either a pressure gauge or a low pressure light on the front of the underside of the boiler, and you will probably not have a hot water cylinder.

You can tell when your radiator needs bleeding - it will be cold at the top but warm at the bottom.

This is caused by trapped air, which can be released by bleeding the radiator with a radiator key. You can buy these from most DIY shops.

If the whole radiator is cold, check that the radiator valve is open. If more than one radiator is cold, the whole heating system may need to be checked by a plumber.

To Bleed the Radiator

  • Turn off the heating system before bleeding to avoid more air entering it.
  • Place the key over the bleed valve (the small square nut at the top end of the radiator) and hold a cloth around it to catch any water. Gently turn the key anti-clockwise until you hear a hiss – this is the air being released.
  • When water starts to come through, turn the key back clockwise to shut the valve off.
  • Don’t unscrew the valve completely as the plug will come right out.

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