How to bleed your radiator

Friday, 15 November 2019   CORGI HomePlan

Are your radiators hot at the bottom and cold at the top? This is a sign that your radiators will need bleeding. The cold patches are caused by air being trapped inside the radiator, and getting rid of it is relatively straightforward. You won’t need an engineer to come out to fix this as it’s something that you can easily do yourself. It’s really quick and simple to do and to help, we’ve prepared a step-by-step guide.


Firstly, here is what you will need to bleed a radiator:

  • A cloth
  • Plastic container to catch the water from your radiator
  • A radiator key or flat head screwdriver - you’ll need to check your radiators to see which you will need

If you have an old radiator you will need a key like this.

If your radiator is modern you will need a flat head screwdriver

How to locate the radiator bleed screw

On the radiator, the bleed screw will be on the right or left hand sides on the top of the radiator.

Some radiators have the bleed screw at the back of the radiator panel. It will be at the top on the right or left hand side.

If you are bleeding a towel rail radiator, the bleed screw will be on the top of the ladder on the right or left hand side. 

It is a relatively simple thing to do, but an important one to help maintain the efficiency of your boiler and central heating system.


How to bleed the radiator

  1. First, switch your heating off and make sure that the radiator is cold.

Top tip: It’s a good idea to bleed your radiators in the morning prior to the central heating starting as leaving overnight to cool down will allow the air to rise to the top of the radiator.

  1. Put a cloth or container underneath the bleed screw and valve at the top corner of the radiator to capture water.
  2. Put the radiator bleed key or screwdriver into the bleed screw turn it anti-clockwise, slowly. You should hear air starting to escape from the valve.

Top tip: When the bleed valve has opened you may see a small hole in the open in the valve. Try and point the hole downwards towards your cloth or container, to catch the escaping water, otherwise it could spray on your walls.

  1. Once all the air has been released, water will start to run out of the radiator valve. When this happens, close the valve by turning the screw clockwise with your radiator key or screw.
  2. With the cloth, wipe down the radiator and around the value to soak up any remaining water.
  3. Turn your heating system on, and your radiator should fully heat.

Automatic bleed valve

Some radiators are fitted with a self-bleeding valve. If the automatic bleed valve does not work and air can not be removed from the radiator, a GasSafe engineer will need to fix it.

If you have a combi boiler or sealed system, you may need to repressurise your boiler after bleeding the radiators.

Purging a radiator

If you’ve attempted to bleed your radiator and it still does not heat up, we can try to purge the affected radiator. Doing this will increase the pressure into the faulty radiator, and opening and closing the thermostatic radiator valve (TRV) will free up a jammed valve spindle.

This is done by closing the TRV on every radiator if possible, except the faulty radiator and one other radiator which will not have a TRV fitted.
When as many TRV’s as possible are closed, switch on your central heating boiler and leave it on for one hour. During this period, open and close the TRV 4/6 times.

After one hour, check if the radiator is heating up then open all the closed radiators on the TRV to your desired setting.


If you have a policy with us and the above advice doesn't solve the problem, please call us at 0800 085 0845.