During the normal heating cycle, the air in your hydronic gas furnace’s water is forced out… This air builds up in the water lines, plus you may start to notice some unregular discrepancies in your gas furnace over time; and air build-up effects in your water lines may range from noisy operations, uneven heating, to total water circulation blockage.
If and when this happens, you have to bleed your hydronic gas furnace to eliminate the trapped air; bleeding is a repair practice usually carried out once or twice a year, and you do not require an HVAC repairman’s help for this routine.
Begin by turning off your gas furnace at the thermostat, and find the bleed valve located on the radiator, furthest from the boiler. These valves are small, cylinder-like fittings that stick up from the supply pipe. They are regularly about an inch tall, with a small nozzle on one side plus a slotted screw head on top. Also, check behind the end cover or a radiator shroud as this HVAC equipment point may conceal them. Place a container under the bleed valve to catch water sputters that will come out through the valve, but slowly open the bleed valve by turning your screw counterclockwise. There should be water sputtering out accompanied by air hissing out through the bleed valve’s nozzle, and do not close the valve until you achieve a steady stream of water flowing out of the valve. If no water pours out of the open bleed valve, you are absolutely dealing with a corroded bleed valve or a closed supply valve line! Call an HVAC specialist to service this problem. After successfully bleeding your gas furnace, turn your screw clockwise to close the bleed valve plus remove the container… Repeat the bleeding process on the next bleed valve. If you have several bleed valves along the entire line, then replace the shroud or cover.