Radiator valves, situated at the end of the radiator, provide the ability to bleed the radiator. This frees trapped air inside, which can impede the heating efficiency of the radiator. Radiator valves are opened by means of a tool called a radiator key which fit into the radiator valve and allow it to be opened in increments for bleeding.
Turn off the power to the radiator boiler. You can do this at the boiler itself or by switching off the boiler power at the main circuit breaker.
Place newspapers or towels on the floor underneath the radiator.
Slip the radiator key over the end of the valve. The radiator key is a small metal shaped tab that fits over the valve at the end of the radiator. If you cannot locate the key, the valve can be opened with an adjustable wrench.
Hold a bowl underneath the radiator valve. This will help catch any water that spills out.
Turn the key or wrench counterclockwise to open the radiator valve.
Radiator water can be quite hot. Wait at least twenty minutes after turning off the radiator boiler before trying to open the radiator.