Bleeding a radiator means letting out any air that has become trapped inside. Trapped air or gas means that the hot water won't be able to get to that bit of your radiator, so it won't heat up.
The good news is, bleeding radiators is a simple job that you can do yourself, and it can make a real difference to how energy-efficient heating in your home is too.
While this isn't a hard thing to do, please follow these instructions with caution. If you don't feel confident about what you're doing, stop and get advice from a qualified heating engineer. Another option is to install an automatic radiator bleeder.
Step 1: Turn your heating on and get your radiators hot
Turn on the heating so that all radiators in your home come on (you may need to turn up the temperature on your thermostat and individual radiator temperature controls to make sure they all come on).
Step 2: Find out which radiators need bleeding
Once your radiators are all hot, go and check each one individually to see if all parts of the radiator are warming up. Be careful - radiators can get very hot and you don't want to burn yourself.
Cool spots, particularly towards the top of the radiator mean that there could be air or gas trapped and you'll need to bleed that radiator.
Air or gas is more likely to get trapped in the highest radiator in the home. It can sometimes get trapped in the coil that runs through the hot water cylinder too, because that can often be the highest point in the system.
Step 3: Bleed the radiators
To bleed most radiators, you will need a radiator key.
To bleed more modern radiators, you can use a flat-blade screwdriver.
At the top of the radiator at one end, there will be a valve.
You can attach the radiator key to the square bit in the centre, or put the end of the screwdriver in to the groove.
Hold the key or screwdriver with a cloth, and have another cloth ready to catch any drips.
Slowly turn the radiator key or screwdriver anti-clockwise.
If gas is escaping, you'll hear a hissing sound will probably be heard.
Once there is no more gas, liquid will come out and the valve will need to be closed quickly. With the more modern screwdriver operated escape valve, liquid is likely to emerge as a jet rather than a dribble, so have that cloth ready and be prepared to use the screwdriver to turn the screw quickly back to the closed position.
Beware, the liquid may be discoloured and could stain carpets if not caught by the cloth. The gas can be flammable, so do not smoke while doing this, and have a window is open nearby.
Step 4: Check the pressure
Check the pressure by having a look at the gauge on your boiler, because bleeding your radiators can cause it to drop
If the pressure is too low, you'll need to 'top up'. You can do this using the lever or tap on your boiler, known as the filling loop.
Afterwards, you may want to run another 'hot test', to check that your efforts have been successful.
Find out more about energy-efficient heating.