Replace air valves on steam heating radiators (or steam mains) if they constantly hiss-out steam when the radiator is already hot, or if the radiator does not get completely hot. Radiator shut-off valves and unions should not hiss at all.
To change an air valve:
- Make sure the boiler is turned off, and that the radiator is cool.
- Turn the old air valve counter-clockwise while looking straight at the valve, and install the correct new valve by screwing it into the radiator threaded hole clockwise until firmly in place, with the venting hole of the air valve on top.
Pipe compound is generally not used on the threads of the air valve, however Teflon®-type tape can be used on the threads of the air valve as long as it does not obstruct the inner hole of the air valve inlet).
Use slower or faster venting air valves on steam radiators to obtain even heating throughout the building. It’s best to leave steam radiator shut-off valves in the 100% open position to avoid water buildup and loud banging noises.