Hello, I have a hydronic heating system with two zones, two pumps at the return to the boiler and had significant problems with ghostflow to the second zone, when the first zone is operating and the second is off. My heating contractor installed two flow check valves in the return before the zone pumps. Even if the flow check valves are closed (clockwise until the end), I am getting a ghostflow several times a day to the second zone. I cannot pinpoint exactly when this happens, but I observed that it happens when the boiler is heating up after a long idle phase. At other times the flow check valve seems to work so it seems to fail temporarily. Is this possible at all? My heating contractor hasn't seen this before and it is hard to demonstrate the issue as does not happen every time. I would appreciate any help. Thanks a lot!
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