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Sep 3, 2016
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Hi, have looked over design given me for controlling this system. 49kw boiler with its own pump to low loss header. then two heating circuits, each with its own programmer, thermostat, pump and 2-port zone valve.
Design shows programmer and thermostat providing switched live for pump and zone valve motor, then switched output from zone valve triggers boiler. I can see this avoids using relays, but I was concerned that it means for a few seconds the pump could be operating against the zone valve until it opens.
thoughts please
 
It's best that way otherwise pump will run on either valve calling giving back feed to the other. Incorporate bypass if worried on secondary circuit. Not an issue if using variable flow pump.
 
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