Hydronic system - pipes BANG when zone shuts down


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Posted by Dale Van Aken on January 04, 1998 at 10:45:25:

I have a new hydronic system with 3 zones (h'well stats). Sometimes (not always - but in the middle of the night seems popular) when a zone satisfies, about 1 sec after I hear the circ stop, the pipes do this LOUD Bang-Bang-bang-bang thing - each bang a little less loud. The sound appears to be pipes flexing (sounds like copper hitting something). I have tried to isolate all combinations of zones and cannot duplicate this by myself (isn't this an engineering rule: "the defect never is visible when you're watching it"?). Anyway, I considered that the circ (Taco 011) might be running too long and trying to pump into a closed valve, but the circ is directly controlled by the zone valves with their outputs (N-switch?) in parallel. I don't see how the circ could run too long unless the timing in the zone valve is on the hairy edge, or inconsistent. Do zones valves fail in this manner? I've never had H'well ones before. Even if this is the case, can a circ like this create enough head to bang the pipes hard? I thought that they were able to run even against resistance. This is waking the kids and bothering the wife (which of course, is why I have to fix it!). I know there are soem real boiler pro's out there. Any ideas? Thanks.



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