It's not uncommon for one or more household radiators to remain cool or lukewarm, while the remaining radiators get hot. This issue is often caused by trapped air – but can easily be remedied by bleeding the radiator(s) in question.

1. Switch on your heating system

Firstly, turn your radiators on. This is necessary to build up the pressure in order to force the air out of the heating system. Wait until your radiators are hot before moving on to the next stage.

2. Check your radiators for cool areas

Now you need to find out if any of the radiators are not working as they should. Check that each radiator is hot, taking care not to burn your hand as you do so. If you find a cool area, it could mean that air is trapped inside. Having located the cool spot, you can move on to step three.

3. Bleed the radiator(s) in question

Now you should switch off your heating system so as to avoid being burnt when you bleed the radiator that has trapped air inside. You will need a radiator key, which you can buy from your local hardware store. Alternatively, you can use a flat-blade screwdriver.

Locate the small valve at the top of the radiator and insert the key or screwdriver. Hold a cloth over the key or screwdriver, and have another cloth handy to absorb the resulting drips. Any hissing sound will be air escaping from the radiator.

As all the air is released, liquid will begin to come out. At this point you should close the valve swiftly. Some more modern radiators have screwdriver-operated valves, which usually force water out as a jet, rather than a dribble.

4. Check the pressure of your heating system

Check the pressure on your boiler. If it is too low, you will need to 'top it up' by using a special tap or level on your boiler. This is called ‘the filling loop’.

Once you’ve finished, it’s a good idea to test the radiators to see if they heat up properly now.


Find out how can help you in a central heating emergency. always recommends seeking the services of a professional tradesperson If you're not entirely comfortable carrying out repairs or maintenance by yourself.