To troubleshoot a steam boiler valve, begin by identifying the specific problem. Common problems with radiator air valves include the valve's failure to close or becoming shut, a gurgling or hissing noise, or leakage and spitting of water.
If a steam radiator's air valve is stuck shut, then cold air gets trapped inside and the radiator doesn't get hot. If it is stuck open, then it hisses constantly. If the air valve spits or leaks water, it may be partially blocked with dirt or debris. To solve any of these problems, clean the air valve; doing so may return it to normal function. If cleaning the air valve does not make it open and close properly, it needs to be replaced.
Air valves that emit a loud gurgling noise indicate that the air supply valve may be blocked, partially closed, broken or improperly installed. Another possibility is that the radiator is improperly sloped, impeding its function or causing sediment to settle into the air valve. The proper pitch is 1 inch for every 10 feet to the supply pipe and valve. Examine the air supply valve carefully for cracks or improper installation, and clean it carefully. If cleaning does not remedy the problem, the valve needs to be replaced.