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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
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Pictures of the piping would also help determine what else might be hapening
Theory and reality don't always align. Most of the time it does, but you have a situation where it does not. I have had this hapen to me before.
The solution is more resistance on the zoned secondary. Either another anti flow device, such as a flow control valve, or a physical zone valve that opens first, then an end switch to start the pump.
If you have a properly sized and installed separator, it is almost unheard of to get secondary side ghost flow? I have seen it on primary secondary piping however. I'd always check both S&R on P/S takeoff tees.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
Its worth a try anyway, before making any major piping alterations.