How to Bleed a Radiator

You only need three things: a radiator bleed key (available for about £1 from any hardware store), a cloth or small towel to catch any drips, and a small container to catch water.

Step 1: Turn on your heating and wait until all radiators are fully warm. Check each one for cold spots at the top — these indicate trapped air.

Step 2: Turn the heating off and wait 10–15 minutes for the system to cool slightly. This prevents hot water from spraying out when you open the valve.

Step 3: Locate the bleed valve — it's usually at the top corner of the radiator, appearing as a small square socket inside a round nut.

Step 4: Place your cloth underneath, insert the bleed key, and turn anti-clockwise about a quarter turn. You'll hear hissing as trapped air escapes. Don't unscrew it completely.

Step 5: When the hissing stops and water starts to dribble out, close the valve by turning the key clockwise. Tighten it snug but don't over-tighten.

Step 6: Check your boiler pressure gauge — it should read between 1.0 and 1.5 bar. If it's dropped below 1.0, top it up using the filling loop as described in your boiler manual.

If you find yourself needing to bleed radiators frequently, there may be an underlying issue. This could be a leak somewhere in the system, a faulty component, or air constantly entering the pipework. A qualified engineer should diagnose the root cause rather than you repeatedly bleeding the radiators.