How to bleed a radiator

It may be something which fills you with dread, but bleeding a radiator is actually quite simple and something you can do yourself


You can improve your heating output and cut your energy bills by bleeding your radiators.

If you find your gas central heating system isn't warming your house enough it could be because there's air trapped in the system, so you should try bleeding the radiators - this will let out any trapped air. 

However, before you start, do a couple of checks to make sure there isn't an underlying problem such as a leak; any signs of rust or water underneath your radiators could signal this issue.

How to bleed a radiator in five steps

If you need to bleed a radiator just follow these five steps carefully.

  1. Check each radiator individually
  2. Turn off the heat
  3. Release the air
  4. Listen for escaping air
  5. Check the pressure

Check the radiators individually

Check radiators

Most radiators occasionally need bleeding to allow hot water to fully circulate. If your radiators are taking a long time to heat up or feel hot at the bottom and cold at the top then it is time to bleed the radiators.

Turn off the heat

Turn off radiator heat

This is very important, boiling water could result in injury and a ruined floor. Be sure to get some old towels at the ready, just in case.

Release the air

Radiator bleed key

You will need a radiator bleed key to do this and finding yours may be the most stressful part! However, you can buy a key from any DIY store or online. They look something like the picture below. For more modern radiators a flat blade screw driver will work just as well. Make sure you have some old rags to hand for the next part.

Fit the key in to the groove of the valve that is at the top of your radiator. Have a rag ready underneath to catch any drips. Use the other rag to protect your hands or just wear suitable gloves. Then, slowly twist anti-clockwise. You will begin to hear a hissing which is the sound of the air escaping.

Listen for escaping air

As the air escapes, the water will rise to the top of the radiator. As soon as water starts to escape, shut the valve straight away. Then repeat this process as you need to on the remaining radiators.

Check the pressure

Check boiler gauge

Take a look at the boiler gauge. For most boilers it should be around the 1 to 1.5 mark. Turn the heating on to make sure there are no cool spots on the radiators and that's it - you're all done!

If you still don't feel confident then don't try anything you aren't comfortable with, ask a friend or family member for help. If you find bleeding the radiators hasn't solved your heating problem then you may need to contact a heating engineer. You can find a trusted engineer in your area through Trustatrader

For odd jobs around the home, take a look at our DIY maintenance planner to compare the costs of hiring a pro or doing it yourself.