How to Bleed a Radiator

A radiator that is cold at the top may have trapped air. Bleeding it can help, provided the heating is switched off and the radiator has cooled.

When should you bleed a radiator?

If a radiator is warm at the bottom but noticeably cooler at the top, trapped air may be stopping hot water from circulating properly. Gurgling can be another clue. However, a radiator that is cold at the bottom, a whole room that stays cold or repeated pressure loss can have other causes.

You do not need to bleed every radiator routinely if it is heating properly. If you are unsure what is wrong, a heating engineer can assess the system.

What you will need

A suitable radiator key (or the tool specified for your valve), an old cloth and a small container for drips. Do not force a worn or damaged bleed valve.

How to bleed a radiator

1. Turn the heating off. Allow the radiator to cool completely before you start. Hot water can cause burns.
2. Find the bleed valve. It is usually near the top of the radiator at one end. Place the cloth and container beneath it.
3. Open it gently. Turn the valve only slightly, using the correct key or tool. You may hear air escaping; never remove the valve.
4. Close it when water appears. Once air stops escaping and a steady trickle of water appears, close the valve gently. Do not overtighten it.
5. Check the system before restarting. On a sealed heating system, read the boiler pressure when cool and compare it with the manufacturer's instructions. Bleeding can lower pressure. Do not attempt unfamiliar re-pressurising steps; ask a heating engineer if needed.

Once everything is secure and the pressure is appropriate for your system, turn the heating back on and check the radiator over time. There is no fixed five-minute test that works for every installation.

When to get professional help

Call for advice if the valve leaks, the boiler repeatedly loses pressure, radiators remain unevenly heated or you need to bleed them frequently. These may indicate a fault that bleeding alone will not fix. Work involving a gas boiler must be carried out by a suitably Gas Safe registered engineer.

HandyExperts can arrange suitable heating and boiler support. You can also call 0330 912 2323.