If your radiator is warm at the bottom and cold at the top, there is air trapped inside it. Bleeding it releases that air so hot water can fill the radiator properly.

It takes about ten minutes and you need a radiator key and a cloth.

What you need

A radiator bleed key, available from any hardware shop for a pound or two. A cloth or small container. That is it. Some newer radiators take a flat-head screwdriver instead.

Step by step

1. Turn your heating off and let the radiators cool. Bleeding a hot radiator risks scalding you.
2. Start with the radiator furthest from the boiler, and if you have two floors, work through the downstairs ones first.
3. Find the bleed valve, a small square nut at the top of one end.
4. Hold your cloth underneath and turn the key anticlockwise a quarter turn. You will hear hissing as air escapes.
5. Wait for the hiss to stop and water to trickle out. Close the valve immediately, turning clockwise. Do not overtighten.
6. Repeat for every radiator, working towards the boiler.
7. Check your boiler pressure. Bleeding releases water as well as air, so pressure will have dropped. Top it back to 1 to 1.5 bar if needed.

The step most people miss

If the radiator is still cold after bleeding

If the top is now warm but the bottom is cold, that is not air. It is sludge, a build-up of corrosion sitting in the bottom of the radiator blocking flow. Bleeding will not shift it and it will get worse.

That normally needs a power flush, which cleans the whole system rather than one radiator.

If no water comes out when you open the valve at all, the radiator valves may be closed or the system pressure may be too low to begin with.

How often should you bleed radiators

Once a year, before the heating season, is plenty for most homes. If you are having to do it every few months, air is getting in from somewhere and that is worth investigating.

When to call someone

• Bleeding does not fix it
• Several radiators are cold at the bottom
• The boiler loses pressure repeatedly afterwards
• The water coming out is very dark, which indicates significant corrosion

How Vantage can help

We cover Hertfordshire, Bedfordshire and Cambridgeshire, we are Gas Safe registered, and we carry out power flushing if your system needs more than bleeding.

Frequently asked questions

Which radiator do I bleed first?

The one furthest from the boiler, downstairs first if you have two floors.

Should the heating be on or off?

Off and cool. Bleeding a hot radiator can scald.

Why is water coming out brown?

Corrosion in the system. It is worth having it looked at.

Do I need to bleed radiators every year?

Once before winter is usually enough.

Want it sorted properly?

If the fault keeps returning after a reset, it is telling you something is degrading rather than broken. Call 01462 506374 and we will diagnose it properly rather than swapping parts and hoping. Gas Safe registered 956889, 12 months on our own labour.