Radiators need to be bled if:
a) They are colder at the top than they are at the bottom
b) If they are cool all over
c) If they are cooler than the heating setting
Bleeding a radiator is one of the easiest jobs to do in the home and is a good way to save money on your energy bill by making your heating system work more efficiently.
Turn off your central heating system and allow water to cool down. This will prevent injury to yourself. Do not attempt to bleed a radiator if the water is still hot.
Fit your vent key into the bleed valve, normally at the side of the radiator.
Top Tip: Place a bowl under the valve in case water leaks out.
Holding a cloth beneath the valve and the key, turn the key anticlockwise and allow the air hiss out of the valve. Turn the key slowly so you have control if water comes out. DO NOT TURN THE VALVE FULLY. A quarter to half a turn will generally do.
Keep the valve open until water starts to bubble from the valve. Then turn the key clockwise to close the valve.
Turn on the central heating to see if the radiator is heating to the right temperature all over.