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How to bleed a radiator | A guide

In this easy Advice Centre guide, we’ll show you how to bleed a radiator and remove air from your heating system to help you keep home nice and cosy all year round.

What does bleeding a radiator mean?

Bleeding a radiator means releasing air that has become trapped inside your heating system.

Letting this air out will help you to heat your home more effectively and reduce your energy bills.

If you can hear pipes banging or radiators gurgling, this is usually a sign that you should bleed your radiator.

Venting your heating system is easy to do, just follow the steps below to fix the problem, save money and create a warm and cosy home that you can put your feet up in.

A woman's feet raised up on to a radiator with snow visible through a window


Having a warm & toasty radiator is a must in winter

When should you bleed a radiator?

If you feel any cold spots

Bleeding a radiator is required if it is not working as efficiently or as effectively as you want it to. You can tell if this is the case by feeling the surface of your radiator. In many cases, you’ll find a cold spot around the top of the radiator surface, and could find that your radiator doesn’t get hot at all. If you experience anything like this with your radiators, the chances are that you’ll need to take steps to remove the air by bleeding the radiator. 

If your radiator is making noises

Another signal that you may have air building up and need to bleed your radiator is when you can hear clanging or prolonged groaning when you switch on your central heating. There could also be other causes for your radiator to make noise, but generally, if you have a clunk or a clang in your heating system, its because you need to bleed your radiators.


How to bleed a radiator in 12 easy steps

Follow our simple 12 step guide for how to bleed a radiator and your radiators should be piping hot and noise-free in no time.

You will need –

  • A radiator bleed key
  • A cloth to catch any water leakage
  • A container or towel to place under the radiator

Follow the quick step summary, or use the video and in-depth guide below to help you to bleed your radiator!

  • Turn the central heating on
  • Check all radiators for cold spots
  • Turn the central heating off
  • Find the first radiator To bleed
  • Locate the bleed valve on that radiator
  • Put a towel on the floor under the radiator
  • Insert the radiator bleed key
  • Turn the key anti-clockwise & listen for a hiss
  • Wait for the hissing to stop & turn the key back again
  • Bleed other radiators that require bleeding
  • Check boiler pressure
  • Turn the central heating back on

A step-by-step guide on how to bleed a radiator

Time needed: 20 minutes.

Please note – This time is approximate and it will probably take longer if you are bleeding more than one radiator.

A step-by-step guide for bleeding hot water radiators.

  1. Turn the heating on full

    First of all, switch on your heating system and wait until your radiators have reached their maximum heat.

    A heating system being switched on via the wall thermostat
    This will help you to feel any cold spots and therefore identify which radiators need bleeding.

  2. Check each radiator for cold spots

    Carefully run your hand along the top of each radiator. If you feel any cold areas, that is a sign that the radiator needs bleeding.

    a hand touching the top of a radiator

    Make a note of which radiators need bleeding as you go through the house.

  3. Turn the heating off and allow it to cool down

    It is important to turn the heating off and allow the radiators time to cool.

    This is to make sure that the hot water in the radiators doesn’t burn you when you start to bleed the radiators.

    boiler dial

  4. Find the first radiator to bleed

    If you find that you need to bleed more than one radiator, always start with the one on the ground floor that is furthest away from the boiler.

  5. Locate the radiator bleed valve

    You will usually be able to find the bleed valve at the top and side of your radiator.

    a man opening the bleed valve of a radiator with his right hand
    The bleed valve is the small metal square or screw found inside the surrounding nut.

  6. Place a tray or a towel on the floor

    Put your container or towel on the floor beneath the bleed valve.

    Convector Radiator_8_Towels and bowl under valve
    This is to catch any drips and protect your flooring from any discoloured water.

  7. Insert the radiator bleed key

    Take your radiator bleed key and insert it into the bleed valve until they have locked together.

    inserting the radiator bleed key into the valve

    Hold your cloth next to the valve and under the little drain hole and be ready to catch any drips.

  8. Make a quarter (anti-clockwise) turn

    Slowly turn the bleed key anti-clockwise to open the valve.

    This will allow the air to escape and you should start to hear a hissing sound.

    Keep turning the valve until it is a quarter to a half of the way open.

    Make sure to not open the valve to fully to avoid water escaping too quickly.

  9. Close the radiator bleed valve

    Once the hissing noise and air stop – and water starts to leak out – you will have bled all the trapped air from the radiator

    water beginning to come out of a radiator bleed valve

    Turn the bleed key clockwise to close the valve.

    Make sure not to close the valve too tightly to avoid damaging the valve.

  10. Bleed your other radiators

    Repeat this process for any other radiators in your home that need bleeding.

  11. Check the pressure of your boiler

    If you have a pressurised central heating system you may notice that the pressure gauge on your boiler has dropped since bleeding your radiators.

    boiler pressure going back up

    If that’s the case, you will need to top the boiler pressure back up before turning the heating back on.

  12. Turn your heating back on for your final checks

    Once your boiler pressure is back to normal, you can switch your heating back on.

    Give your radiators some time to heat up and check to see if there are any cold spots.

    If you find that there are still some cold patches at the top of the radiator, try bleeding the radiator again.

Does Your Radiator Still Have Cold Spots?

A radiator that requires bleeding will have cold patches at the TOP.

But, if after you bleed your radiator there are cold spots across the bottom, this could be a sign that you have a build up of sediment inside the appliance – therefore you may need to flush the system.

Take a look at our guide to help you remove sludge and limescale from your heating system and fix your cold radiators.

a graphic that shows a radiator that is cold at the top and warm at the bottom

How To Bleed A Radiator – Frequently Asked Questions

Do You Bleed Your Radiators With The Heating On Or Off?

You should always bleed your radiators when the heating is switched off and the system has cooled down, because bleeding radiators with hot water flowing through the system increases the risk of scalds and burns.

Which Radiators Do You Bleed First?

If your home has more than two floors, begin by bleeding the downstairs radiators first – start with the one that is furthest away from your boiler.

How Often Should You Bleed Your Radiators?

Hot water radiators should be bled at least once a year.

It is always best to do this well in advance of the winter months so your system can be ready and be in full working order before the temperature begins to drop.

How Long Should It Take To Bleed A Radiator?

The average radiator should take no more than 20 to 30 seconds to bleed in full. This can vary with the size of the radiator and the amount of air trapped inside.

Simply carry on bleeding the radiator until the hissing noise has stopped and water begins to run out of the bleed valve. This means that you have bled all of the air out of the radiator.

Where Can I Buy A Radiator Bleed Key?

Radiator keys are easy to get your hands on.

Most hardware stores will stock them, and prices range from anywhere between 50p to a fiver.

The Very Best Heating Advice From BestHeating.com

If you’re having trouble with your heating, want to move a radiator or decorate behind it, or perhaps fix a leak, make a change or improve your interior design, we have a guide to help you do just about anything radiator related.

Don’t let your heating get you down, discover a wealth of expert heating advice with BestHeating.com.

Please note: Our ‘How-To’ manuals are intended only as a guide to assist you with common home heating tasks. Please do not attempt to undertake this task if any of the instructions are unclear, or if you are in any doubt about what to do. Instead, seek advice from a professional.

How to bleed a radiator video

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