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How to bleed a radiator

Posted on 2/24/2020

If one of your radiators is making a funny noise, heating up in patches, not getting hot enough or simply not heating up at all, it might need to be bled. Here you can learn how to bleed a radiator safely and easily.

What is bleeding a radiator?

When you bleed a radiator, you’re essentially letting out any air trapped inside. Trapped air prevents water from thoroughly heating a radiator and it often leaves it cold in patches, usually at the top.

Your radiator probably needs bleeding if it's making a 'whooshing' noise or not heating properly or evenly

One way to identify if your radiator needs bleeding is if it’s making a ‘whooshing’ or a gurgling sound, which is the sound of the water rushing through/around the trapped air.

It’s important to get this minor problem fixed because it could mean you’re paying to heat your home but not enjoying all the heat. Luckily, bleeding a radiator is a simple task that even inexperienced DIYers can handle.

So, let’s bleed that radiator!

What do you need?

All you need is:

  • A radiator bleed key/screwdriver – many newer models of radiator have valves which can be opened using just a screwdriver, but for older ones you might need a radiator bleed key. Radiator bleed keys can be found at virtually any hardware store
  • A cloth or towel – to catch spraying water and wipe any away
  • A bucket/container – to catch dripping water
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    How to bleed a radiator

    1. Turn your heating on

      First, turn on the heating. This will build up the pressure in your radiator and help the air escape when you come to bleed it. It will also help you identify which radiators need bleeding.

    2. Work out which need bleeding

      You might have noticed one of them isn’t heating properly, but there could be more. So, once they’ve warmed up, go through your whole house and check each radiator for cold spots and peculiar sounds.

    3. Turn off your central heating

      Once you’ve identified which radiator(s) need bleeding, turn off the system. This is because when you get to bleeding them, it’s best that the water inside isn’t too hot, just in case some leaks or sprays onto your skin.

    4. Pick the right radiator first

      If you’re bleeding more than one radiator, it’s best to start on the ground floor and work up. This is because as you’re working through them releasing trapped air, any air left over will most likely rise through the system.

    5. If you're bleeding multiple radiators, start from the ground floor or lowest radiator and work upwards

    6. Prepare the area

      The water in your system may be brownish in colour, so make sure you have your cloth and bucket ready to catch any that escapes.

    7. Bleeding a radiator Open your radiator valve by turning your key or screwdriver anti-clockwise
    8. Open up the radiator bleed valve

      Attach either your bleed key or screwdriver to the bleed valve, which is usually found at one of the top corners of the radiator. Turn it anti-clockwise (a quarter to half a turn should be enough) until you hear a hissing sound.

    9. Bleeding the radiator

      This hissing sound is the air escaping. The air could be hot, so make sure to keep your distance. Also, never fully open the valve because the water could flow out quickly and drop your system’s pressure.

    10. Close the valve

      Once all the air is out and water begins to appear, close the valve by turning it clockwise, making sure you don’t over tighten it. Repeat this process on any other radiators you think might have trapped air (remember to work upwards through your house).

    11. Escaping air and water could be hot, make sure to keep your distance and cover the hole with your towel to prevent spray

    12. Check the pressure of your heating system

      Once you’ve bled all your radiators, it’s a good idea to check your system’s pressure. If while bleeding your radiators you released minimal amounts of water and maintained the correct pressure, the gauge on your boiler should be pointing towards green. If you’ve altered the pressure too much, check out our page on how to repressurise your boiler.

    Should you get a professional in?

    If you don’t want to take on the task bleeding a radiator, that’s fine. Just get help from a professional plumber or boiler engineer. We can put you in touch with a qualified and friendly Local Hero. Just fill in the ‘What needs doing?’ field below and they can pop around to bleed your radiators as quick as a flash.

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