How to Purge the Air From Zone Valves


Hot water boilers and heating systems use piping to transport hot water to different parts of buildings. These areas are called zones, and each zone has its own supply line, air bleed or purge valve, thermostat and radiator or baseboard. A problem that arises with closed-loop piping systems is that they can accumulate air, stopping the flow of heating water to one or multiple zones. Zone valves can be purged of air, starting the flow again. You only need some basic tools to purge the zone valves in your heating system.

Things You'll Need

  • Heating system technical manual
  • Bucket
  • End wrenches
  • Penetrating oil
  • Rags
  • Turn your heating system on and raise the thermostat temperature 15 degrees hotter than normal. Let it run for 10 minutes until the radiator piping is warm to the touch. Follow the piping on each zone you have, if there are multiple lines serving different parts of the building.

  • Listen very carefully for bubbling, surging or obvious water movement within the pipe or pipes. This denotes air in the system and it must be purged. If some heating pipes are cold and others are hot at the same thermostat temperature, it could indicate an air blockage.

  • Locate your air drain-purge valve or valves on your system, relevant to the pipeline which exhibited the surging noise. Consult your heating system technical manual for their exact location. Some valves might be located on the line near the radiator or on the baseboard. Look for a cap nut on a roundish stem, protruding from the pipe.

  • Wet the valve bleeder nut with penetrating oil several times for a duration of two hours. Wipe up any excess oil from the valve and from the floor with a rag. This will free up any corrosion and allow the valve to open.

  • Place a bucket under the bleeder zone valve to catch any water runoff. Use an end wrench to open the bleeder zone valve, just enough until you can hear air escaping. If no air or water escapes, gently probe the bleeder hole with a paperclip, but do not stab deep into it. Let all air escape and then close the valve. The pressure on the gauge should read 15 to 20 psi.

  • Perform the same function on the rest of the zone valves. With the boiler running, feel for heat on all the pipes -- they should all be uniformly warm and there should be no gurgling or surging noises.

Tips & Warnings

  • Stand away from escaping air and water from the zone valve when you loosen it. It can scald and cause injury.

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