Bleed a radiator — HomeGraft

Release trapped air from a radiator so it heats up fully, top to bottom.

BR-01Turn the heating on and find the cold radiatorPut the heating on and let radiators warm up for 10-15 minutes. Feel each one with your hand. A radiator that's cold at the top but hot at the bottom has trapped air and needs bleeding. Note which radiators need doing before you start.

BR-02Turn the heating offSwitch the heating off at the thermostat or programmer and let the system settle for a few minutes. Bleeding a hot, pressurised radiator can spit hot water, so give it a little time to cool slightly first.

BR-03Get your tools readyFind the bleed valve, a small square or slotted point at the top corner of the radiator, opposite the flow valve. Have a radiator bleed key, an old cloth, and a small container or jam jar to hand to catch drips.

1 each · Radiator bleed key

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1 each · Old cloth or rag

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1 each · Small container (jam jar or similar)

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BR-04Hold the cloth ready and open the valve slowlyHold the cloth under the valve to catch drips. Fit the bleed key onto the valve and turn it a quarter turn anticlockwise, slowly. You'll hear a hissing sound as trapped air escapes. Keep it steady and don't open it fully.

BR-05Close the valve once water flows steadilyWhen the hissing stops and water starts to dribble out steadily with no more air, close the valve straight away by turning it clockwise until snug. Don't overtighten it. Wipe away any drips with the cloth.

BR-06Check the boiler pressure gaugeBleeding a radiator lets a little water out of the system, which can drop the boiler pressure. Check the pressure gauge on your boiler. If it's below the manufacturer's minimum (often marked in a green zone, usually around 1 bar), top it up using the boiler's filling loop, following the instructions on or near the boiler.

BR-07Turn the heating back on and checkSwitch the heating back on and let it run for 15-20 minutes. Feel the radiator again, it should now be evenly hot from top to bottom. Check the bleed valve for any leaks and tighten gently if needed.

BR-08Tidy upDry off any splashes around the valve and skirting with the cloth. Put the bleed key somewhere handy, you'll likely need it again for other radiators or another time.

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