How to bleed a radiator

Discover how to bleed a radiator to get rid of cold spots and annoying gurgling

How to bleed a radiator
How to bleed a radiator
(Image credit: Paladin)

Knowing how to bleed a radiator is a must – and when you're spending lots of time at home it's even more important to know what to do. There are some clear signs that indicate when your radiators need bleeding and it's the trapped air that builds up in your central heating system which can stop them from working efficiently. 

Air prevents water from reaching the whole radiator, so you may begin to notice that the radiators upstairs aren’t getting as hot as those downstairs, or that there are cold patches on some of them. Annoying gurgling sounds are also an indicator that you need to release some trapped air.

We’ve created a simple five-step guide on what is essentially removing air from your central heating system, whether you’re in a two storey house or a one bed flat. Watch the video below, or read on.

What you need:

  • Two old towels
  • A plastic tub
  • Radiator key
  • An old cloth

Equipment for bleeding a radiator

1. Identify whether your radiators need bleeding

To do this, start by turning your central heating system on and then check individual radiators (using the old cloth can help to not burn your hands) by running your hands over the top of them. If you spot any of the following, the chances are that air has built up inside your radiators and that they will benefit from bleeding.

  • The metal is cooler at the top than the bottom
  • You find any cold patches
  • Any condensation or damp patches surrounding it
  • Odd creaky noises and vibrations

2. Switch off the heating

Once you know which radiators need bleeding, you will then need to 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. Check your boiler pressure

This is an important step as you lose water when you bleed your radiators, so it’s normal for your boiler pressure to slightly decrease. As a guideline, 1.0 – 1.5 bars when off and 2 bars when switched on is about right. If yours seems to have dropped too low, then you may need to repressurise your heating system. 

If all looks swell, then head to the final step. 

replacing a radiator valve

5. Do the 'heat test'

If your boiler pressure looks good then it’s time to do the ‘heat test’ by switching the heating back on and checking the radiators for improvements. There should be zero cold patches or signs of the initial problems you spotted, which means that your efforts have paid off and that you can go back to those cosy nights in.

Tips for bleeding a radiator

  • If the valve comes out, use an adjustable spanner to replace it.
  • Once you’ve finished bleeding the radiators, you can use your boiler's instructions when checking the pressure of your heating system.
  • 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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