Sport
How to Bleed a Radiator: A Simple Step-by-Step Guide
Cold patches at the top of your radiators? Trapped air is the culprit. Here is how to bleed them safely in five minutes.
Sarah Mitchell
Energy Efficiency Advisor06 Jul 2026Updated: 06 Jul 20263 min read
Key takeaways
Reading time — 3 min
Expert reviewed — Practical guidance from our heating team
When a radiator is cold at the top but warm at the bottom, trapped air is stopping hot water from filling it. Bleeding releases that air and restores full heat — and it is one of the few heating jobs you can safely do yourself.
What you will need
- A radiator bleed key (or a flat-head screwdriver on newer valves).
- A cloth and a small container to catch drips.
- Five spare minutes with the heating switched off and cooled.
The steps
- Turn the heating off and let the radiators cool completely.
- Find the bleed valve at the top corner of the radiator.
- Turn the key slowly anticlockwise until you hear a hiss of escaping air.
- When water trickles out, close the valve firmly and wipe up.
- Re-check the boiler pressure and top up to 1–1.5 bar if needed.
When to call an engineer
If radiators need bleeding again and again, or the cold patch is at the bottom, air is not the issue — you likely have sludge or a circulation fault that needs a professional look.