How to bleed a radiator

Does it need bleeding?

If a radiator is cold at the top but warm at the bottom, or you hear gurgling, air is trapped inside. Letting it out helps the radiator heat properly.

Step by step

1. 1Turn the heating off and let the radiators cool down.
2. 2Hold a cloth under the bleed valve (the small square nut at the top corner).
3. 3Turn the valve anticlockwise with a radiator key about a quarter turn. You'll hear air hiss out.
4. 4When water starts to come out, close the valve again.
5. 5Check your boiler pressure gauge — if it has dropped below the level in your boiler manual (often around 1–1.5 bar), top it up using the filling loop as the manual describes.
6. 6Turn the heating back on and check the radiator warms evenly.

If it's still cold

A radiator that's cold at the bottom usually has sludge build-up, and one that stays cold entirely may have a stuck valve. Those are jobs for a heating engineer.