Curious if the one that was open is on the affected zone. These valves
prevent backflow and if left open, allow the zone to work by gravity. Try
closing them all




"Max" wrote in message
...
There are flow check valves installed...just a little further down the
line. I had some trouble loosening all but one screw as they wouldn't
budge. Not sure if they should be left open or screwed tight? One is
open, the others are closed or mostly closed.

The system did work just fine.

I'm not sure if it's an issue, but the circ pumps pull, not push.

I have created a line diagram of the system you can see he
http://www.advantechcny.com/diag.pdf

Thanks for your help so far. I'll shut off the zone above the pump
tonight and see what happens overnight.