How to bleed a radiator — step by step
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Turn the heating on and allow the system to fully warm up (15–20 minutes). This allows air to collect at the tops of radiators where the bleed valve is.
Starting with the radiator furthest from the boiler, insert the bleed key into the square slot on the bleed valve (usually at the top, back corner of the radiator).
Turn the key anti-clockwise slowly — a quarter to half turn. Hold a cloth beneath the valve. You will hear hissing as air escapes.
As soon as water trickles steadily from the valve — with no air sputtering — close it firmly clockwise. Do not overtighten; the valve seat is soft and can be damaged.
Work through all radiators from furthest to nearest to the boiler.
After bleeding, check the boiler pressure gauge. Bleeding releases water and drops the system pressure. Repressurise to 1–1.5 bar using the filling loop if the gauge has dropped below 1 bar.
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