What you need

A radiator key from any hardware shop, and an old cloth.

Step by step

  1. Turn the heating off and let the radiators cool
  2. Hold the cloth under the small valve at the top corner of the radiator
  3. Turn the key a quarter turn anticlockwise and listen for the hiss of air
  4. Close the valve as soon as water appears
  5. Repeat for each radiator, starting downstairs

Check the boiler pressure

Bleeding radiators lets a little water out of the system. Look at the boiler gauge afterwards and top it up to about 1.2 bar if it has dropped.

If it does not help

A radiator that stays cold after bleeding may have sludge inside. A power flush clears it, and we can quote for that on the same visit.