Radiator Problems

Bleeding a radiator

If the top part of a radiator is cold, this is because air is trapped in the system. Bleeding the radiator releases this air and allows hot water to fill the whole system.

Do not bleed if

Do not bleed the radiators if you have a combination boiler: this type of boiler will have either a pressure gauge or a low pressure light on the front of the boiler, and you will probably not have a hot water cylinder.

Before bleeding

  • If the whole radiator is cold, check that the radiator valve is open. If more than one radiator is cold, the whole heating system will need to be checked by a plumber.
  • Turn off the heating system before bleeding; otherwise the pump might draw more air into the system.
  • You will need a special radiator key, available from most DIY and hardware shops. You will also need a rag or cloth and a bucket or bowl.

How to bleed

The bleed valve is the small square nut at the top end of the radiator. Place the key over the valve and hold the 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. DO NOT unscrew the valve completely as the plug will come right out.