How to bleed a radiator

Over time, air can build up in your heating system, which will stop it from working efficiently. Here's a step-by-step guide to bleeding a radiator to release the trapped air

Traditional radiator in living room
(Image credit: Castrads)

As air builds up in your central heating system, your radiators may begin to gurgle and develop cold patches that stop them working efficiently. If you live in a two-storey house, you may begin to notice that the radiators upstairs aren’t getting as hot as those downstairs. To counteract this, you will need to learn how to bleed your radiators, which releases the trapped air.

If you’ve started to notice issues with your radiators, follow our simple step-by-step tutorial on bleeding them to restore efficiency and make sure they are working properly.

What you’ll need:

  • Two old towels
  • A plastic tub
  • Radiator key

Equipment for bleeding a radiator

1. Check if your radiator needs bleeding

To check if you need to bleed a radiator, run your hands over it when the central heating is on, being careful not to burn your hands. If the metal is cooler at the top than the bottom, or has cold patches, chances are air has built up inside.

2. Switch off the heating

Firstly, switch your central heating  off at the boiler and wait for the radiators to cool down completely. While you’re waiting, lay one towel on the floor to protect it and wedge another behind the radiator to catch any water that leaks out.

3. Check the valve

To locate the valve, check the top edge of the radiator – the release valve looks like a small, square pin. Place the radiator key into the release valve and carefully twist it anti-clockwise. You’ll hear a hiss as the trapped air is released, which will take a few seconds. Once you hear a gurgling sound or water begins to come out, you’ll need to twist the key clockwise to close the valve. Use the towel or plastic tub to catch an excess water that leaks out. Repeat the process on any other radiators that need bleeding.

Using a radiator key

4. Switch the heating back on

Then, switch the heating back on and check the radiators to ensure no cold spots remain.

replacing a radiator valve

Tips for bleeding a radiator

  • If the valve comes out, use an adjustable spanner to replace it.
  • Once you’ve finished bleeding the radiators, check the pressure of your heating system is okay using your boiler’s instructions.
  • If you have double-panel radiators you will need to bleed both panels.

Lead image: Rococo II 760mm 10 sections in Full Polish finish with wall stay, Chatsworth thermostatic valve, shrouds and base plates (all Satin Nickel), £955.20, Castrads

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