Can anyone briefly explain how a P74FA-5 proves flow to a heating coil for an air handler. Hot water is is modulated from a 3-way mixing valve, to the circ. pump and then to the coil. Pressure inputs are on the suction and discharge side of the pump. CO is set at 20 psi. The circ. pump is running and there is proof of run status. Alarm on EMS states no flow.
Need a simple explanation of how the switch should work and be set. I believe the fixed diff. is 1.5.
Thanks in advance.