How to Clean a Steam Radiator Air Vent

Heating systems that feature boilers and radiators can be hot water or steam systems. Hot water systems heat rooms by pumping hot water through the radiator, where the heat is radiated out into the room before the water flows back to the boiler. Hot water systems always have two pipes attached to the radiator, one at each end near the bottom.

Radiators for steam systems look similar to hot water radiators, but they operate through the flow of gaseous steam vapor rather than hot water. Radiators for these systems may use one pipe or two pipes. If your steam system uses a one-pipe system, the radiators will be mounted with air vents that need to be periodically cleaned.

How Single-Pipe Steam Systems Work

In the two-pipe steam system, there is one network of pipes that distribute steam outward from the boiler to the radiators, and separate pipes that collect the condensed steam as it turns back to water. In a single-pipe system, however, a single pipe both delivers steam outward to the radiator and collects the moisture that condenses and transports it back to the boiler. The single-pipe system depends on special one-way radiator vents that close when they heat up, ensuring that steam doesn't escape. But when the system cools, the vents must open up to allow free passage of air.

The air vents on radiators for a single-pipe system are usually bullet-shaped devices, pointed on one end. The air vent is located on the opposite side of the radiator from the control valve, which has a twist knob. In single-pipe systems, there is very often a characteristic hissing sound caused by air passing through the air vent. This hissing sound will occur as the system is just beginning to heat up, as well as when the system is cooling down.

During the system's heating cycle, the heat-sensitive air vent closes to contain the steam inside the system and prevent it from escaping into the room. At the beginning of the heating cycle, air within the radiator will escape through the vent, often with the characteristic hissing sound. Then, once the vent senses the high temperature as steam fills the radiator, it closes tightly to contain the steam. As the system cools down again and moisture condenses, the air vent opens again to allow room air back into the system. 

Occasionally the air vent may clog with rust or mineral deposits. Sometimes a troublesome radiator air valve must be replaced, but in many instances, a simple cleaning will restore it to working order, as described in the following steps.