If your radiators are cold at the top but warm at the bottom, or your heating takes ages to warm up, trapped air is usually the culprit. Bleeding a radiator releases that air so hot water can fill the whole radiator again. It's a simple job that takes a few minutes and a radiator bleed key.
Signs your radiators need bleeding
- Cold patches at the top of the radiator while the bottom is warm
- Radiators taking a long time to heat up
- Gurgling or rattling noises from the system
- Some radiators not heating while others do
What you'll need
- A radiator bleed key (cheap from any DIY shop), or a flat-head screwdriver for some valves
- A cloth or small container to catch drips
- Old towels to protect the floor
After bleeding: check your boiler pressure
Bleeding radiators releases water as well as air, which can lower your boiler pressure. Once finished, check the pressure gauge and top it up to around 1–1.5 bar if needed (see our guide on boiler pressure for how).
How to bleed a radiator
- 1
Turn your heating on
Put the heating on so the radiators get hot. This helps you find which ones have cold spots and need bleeding.
- 2
Turn the heating off and let radiators cool
Before bleeding, turn the heating off and let radiators cool so you don't get scalded by hot water.
- 3
Hold the key on the bleed valve
Find the bleed valve at the top corner of the radiator. Put the bleed key on it and hold a cloth underneath.
- 4
Turn slowly anti-clockwise
Turn the key slowly anti-clockwise (about a quarter to half a turn). You'll hear a hiss as air escapes — don't open it fully.
- 5
Close when water appears
As soon as a steady trickle of water comes out instead of air, turn the key clockwise to close the valve. Wipe up any drips.
- 6
Re-check pressure and heating
Turn the heating back on, check the boiler pressure (top up to ~1–1.5 bar if it dropped), and feel the radiator — it should be warm all the way across.