Bleed a radiator

Trapped air prevents your radiators from heating up fully, leaving them feeling cooler at the top than at the bottom. Bleeding your radiators may sound a bit gruesome, but it's a simple process that will help you to get that pesky air out so your radiators can get lovely and toasty.
  1. Switch off the boiler
    First, switch off the circulation pump or just switch off the whole boiler so there's no chance of you getting splashed.
  2. Get a bleed key
    Each radiator has a bleed valve at one of its top corners, identifiable by a square bit in the middle of the round plug. They're turned by radiator keys, which can be bought at any DIY shop.
  3. Open valve
    Use the key to turn the valve anticlockwise about a quarter of a turn. It shouldn't be necessary to turn it further – but have a small container and a couple of rags handy to catch spurting water in case you open the valve too far.
  4. Close the valve
    You will hear a hissing sound as the air escapes. Keep the key on the shank of the valve, then when the hissing stops and the first dribble of water appears close the valve tightly.


If no water or air comes out when you bleed the radiator then the valve is probably blocked with paint.

  1. Close the inlet and outlet valve at each end of the radiator, then remove the screw from the centre of the bleed valve.
  2. Clear the hole with a piece of wire, the reopen one of the radiator valves slightly to eject some water from the hole.
  3. Close the radiator valve again and refit the screw in the bleed valve.
  4. Open both radiator valves and test the bleed valve again.

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