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How could air possibly be getting into a hot water system?

Randy_5 Member Posts: 1
About a month ago I had 2 zone valves installed in my hot water system. Since then I have had problems with air in the line. I have bled off air from one of the zones (actually one radiator in this zone) almost every day since this work was completed and still the banging of pipes continues when the system calls for heat.
I have tried bleeding with the valve from the city water both open and close, neither seem to make any difference.
Any help that could stop the banging would make sleeping easier!


  • Bill Clinton_2
    Bill Clinton_2 Member Posts: 19
    probably not air that's the problem:

    Ten to one those zone valves are in backwards, closing with the flow rather than against. Closing with the flow means the pressure of the flowing water slams those valves shut, causing a sort of water hammer.

  • dann crist_2
    dann crist_2 Member Posts: 37

    if you'r getting air as you "bleed" the system then it is air that causes the problem. "bleeding" the air from a system is most times not an adaquate solution--- it (the air) must be forced through the system. to be Properly done, allow street pressure to flow into the boiler, insuring that the coures of travel for the water is completely through the loop, and out the return side, Water must not be allowed to "short circuit" to the purge valve. do one zone at a time. run the hose from the purge valve into a bucket full of water and allow the water to spill from the bucket to the floor drain, this will allow you to see the air bubbles coming from the system water. repeat a time or two for each zone, or until no bubbles appear. Some guys set up their boilers with a purge valve for each zone (wasetful use of extra valves) Others install one boiler drain in the return line downstream of all zone valves, and upstream of a ball valve in the main return line. Closing off the ball val;ve and opening one zone valve at a time w/ the hose connected to the boiler drain you don't have to switch the hose from one boiler drain to another.
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