How to Bleed a Radiator (Step by Step)

If a radiator is warm at the bottom but cold at the top, air is probably trapped inside. Bleeding the radiator lets the air out so it heats properly again.

What you need

• A radiator key (cheap at hardware stores) or a flat screwdriver for some valves
• An old cloth or towel
• A small container

Step by step

1. Turn the heating on so all radiators warm up, then turn it off and let them cool.
2. Find the bleed valve at the top corner of the radiator.
3. Hold a cloth under the valve.
4. Insert the key and turn it slowly anticlockwise about a quarter turn.
5. You'll hear a hiss as air escapes.
6. When water starts to come out, close the valve.
7. Repeat for other radiators that need it.

Check the boiler pressure

Bleeding radiators can lower the pressure in combi boiler systems. Check the pressure gauge and top it up following your boiler manual if it's below the recommended level.

How often?

Bleed radiators at the start of winter, or whenever you notice cold spots at the top.

If radiators are cold at the bottom instead, there may be sludge build-up, and a heating engineer can help.