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I have a system where I get unwanted flow through my zones. The system is a 399 tt piped with seperator the near boiler piping is 2'' the zone piping is 2'' the seperator is a 4'' . the boiler pump is a 26-150.I have a 30 or 40 gal indirect on there it is piped with close spaced tees on the boiler side . When i get a call for heat on the indirect it pushes water through my Zones the zone pumps. I have s 26-150 at about 20gal a piece for each zone. The indirect has a 26-99 on their. I unpluged my zone pumps. To check the unwanted flow. THANKS FOR YOUR VALUABLE TIME MERRY CHRISTMAS