ranco water heating thermostat

bill_8

i have a hydro heat (PA) water to water GSHP with DHW. the DHW circulator runs 24/7. i have been happy with this unit but i have also been trying for the last 1.5 months to get any kind of answer from them on my question below.

i would like to put a setpoint controller (like the tekmar 150) on the DHW loop to turn on/off the DHW circuit.

from the schematic it shows the ranco WHT relay (C12) has C,NO,NC with a capillary tube in the DHW loop to sense temp. wiring is setup with C and NC that energizes a three way valve all the time until there is a call for DHW heat based on manual setting of ranco WHT (interesting enough you turn the therm counter clockwise to raise the temperature). best i can tell when there is a call for DHW heat the ranco WHT opens the relay thereby de-energizing the three way valve and the GSHP turns on and heats the DHW circuit . the setpoint must be set internally somehow. there are no wires on the NO terminal. the DHW circuit does take priority over heat.

my question. i pulled the wires off the ranco WHT and wired to a NC relay but that did not work. i am missing something on how the ranco WHT relay works. is the Com or NC post somehow grounded to the unit itself?

any insight appreciated. thanx in advance. bill