Plumbing & Heating · 6 min read · Beginner
How to Bleed a Radiator: Release Trapped Air & Check Pressure
Bleed trapped air from a hot-water radiator safely, then check that the system warms evenly and restore boiler pressure only if the system instructions require it.
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Key points & steps
- Turn the heating off and allow the radiator and system water to cool before opening the bleed point. Keep a cloth and small container ready because some water may escape.
- Locate the bleed valve near the top of the radiator and use the correct radiator key or tool. Protect nearby paint and flooring from drips.
- Turn the bleed valve slowly anti-clockwise only enough to let trapped air escape. Do not remove the bleed screw completely.
- Listen for the hiss of air and close the valve gently as soon as a steady trickle of water appears.
- Wipe the valve dry and check it is not leaking. Do not overtighten a small bleed screw in an attempt to stop a damaged valve leaking.
- Turn the heating back on and check that the radiator warms more evenly from bottom to top.
- If you have a sealed heating system, check the boiler pressure against the manufacturer guidance after bleeding and top up only using the correct filling procedure if required.
- If radiators repeatedly collect air, pressure repeatedly falls, the bleed valve leaks or the system has other faults, arrange competent heating-system investigation rather than repeatedly bleeding it.
Practical tips
- Never bleed a radiator while the system is very hot; escaping water can scald.
- A radiator that is cold at the bottom rather than the top may have sludge or a circulation issue rather than trapped air.
- Boiler pressure targets vary by system, so use the appliance instructions rather than one universal pressure number.
What you may need
- Radiator key or correct bleed tool
- Cloth
- Small container
- Boiler/system instructions if pressure may need restoring