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How to bleed your radiator

If your radiator is cold at the top but hot at the bottom it means there’s air in the system and you’ll need to bleed your radiators.

Never bleed your radiators when they’re hot otherwise scalding water could be released.

You will need:

  • A radiator bleed key or screwdriver
  • A cloth

Step 1: Turn off your central heating and wait until the radiators are cool. 

Step 2: All radiators are provided with a bleed valve in one top corner to allow trapped air to be released. It’s a square shaft inside a threaded plug (a round hole with a square inside it). Use a radiator bleed key (or in some cases a flat-head screwdriver) to turn the shaft anti-clockwise to open the valve. This should be between a quarter turn and a half-turn – don’t unscrew it by more than one complete turn.

Step 3: You’ll hear the trapped air hissing as it escapes. Hold a cloth beneath the valve to catch any water, and as soon as the first trickle appears close the valve by turning the bleed key clockwise.

Check all of your radiators as you may need to bleed more than one. 

Turn your heating back on and re-pressurise the boiler if you need to. Your radiators should now work more efficiently. If you find you have to bleed your radiators often, report this repair to us, as there is likely to be a fault somewhere that is allowing air to enter the system.

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