How To Bleed A Radiator

Posted by mprice 19/06/2017 1 Comment(s) Heating,

Bleeding a radiator is required when air gets trapped in a central heating system. By removing this trapped air (bleeding) the efficiency and effectiveness of your heating is greatly improved.

Don't be scared however, as bleeding radiators can be done safely as a DIY project by just following a few basic steps.

Which radiators should I bleed?

The first signs are radiators that are not heating up as much as they should, or have noticeable cool spots. With your central heating turned on, a simple test is to move your hand over the surface of the radiator. If you notice it is warm at the bottom but cool at the top then this would suggest trapped air which can then be released. Take care – radiators can get very hot.

Bleed Valves

Bleed valves are where the air is released and will be located at the top of the radiator, often on the opposite side to the temperature regulator, but this will vary by manufacturer.

There are two types of bleed valve:

  • Screw type
  • Key type


The screw type is found on more modern radiators and simply requires a flat head screwdriver to undo.

Standard Radiator Bleed Key

The key type is normally found on older radiators and requires a special radiator key to undo.

Once you have located the bleed valve and have tools to hand, you're ready to begin.


Bleeding Radiators


  1. Turn the central heating off – allow the radiators to cool to ensure a safe working environment. Ensure any timer settings have also been switched off. If your heating has a header tank, ensure the feed to this is maintained.
  2. Prepare working area – radiator water can be messy. To avoid damaging carpets / flooring we would suggest laying old towels, trays etc under the radiator to soak up any spillages that may occur. Have hand cloths available to use close to the valve.
  3. Open radiator valves - ensure that both the intake and exit valves (bottom right and left) of the radiator are turned to the "open" position.
  4. Undo bleed valve – carefully undo the bleed valve counter-clockwise (no more than half a turn as you don't want it to come out completely) using either the key or screwdriver. Hold a cloth under the valve with your other hand (or a helpful assistant if you have one) to catch any drips.
  5. Release air – any trapped air should now be coming out of the released valve making a hissing sound. Water may splutter out at the same time.
  6. Close bleed valve – when the hissing stops but small amounts of water continue to come out. Turn the valve clockwise quickly and firmly, but do not over-tighten. Dry around the valve and check there are no leaks.
  7. Turn the heating back on – check the boiler pressure settings. Should the pressure be too low, re-pressurize the system following the boiler manufactures guidelines.
  8. Check the radiators – wait until the radiators get up to temperature, and re-test. This simple task should now mean any cool spots have now disappeared. Job well done!

We hope you've enjoyed this post and found it informative, and now you've mastered the art of bleeding a radiator, why not take on your whole house! It's good practice to bleed the whole central heating system once a year. Should this be undertaken, start on the first floor with the radiator furthest from the boiler and then work back to the boiler on the same floor. Repeat the procedure on any upper floors.

Keep your house 'toasty' warm - a well maintained central heating system runs more efficiently, saving both energy and money.

Below you can find a video on how to bleed a radiator courtesy of richard salt youtube channel. We hope you don't mind us using this - please get in touch with us when you see this.

Thanks to Richard Salt for this video on how to bleed a radiator


Don't forget that there are ways for you to protect your heating system. Take a look at some of the great deals we have on water treatment products that will clean out your system and protect it for years to come

1 Comment(s)

Peter cafferty:
29/06/2017, 03:52:59 PM

Useful info thank you

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