weird thermostat voltage issue

Thread Starter


Joined Oct 10, 2009
I'm trying to figure out an issue on a thermostat connected to a zone control board that's connected to a Water Source Heat Pump. See attached wiring diagram.

Existing thermostat(White Rabbit TP32W02) works on any connector: Unit, P9, P1, P2, P3 or P4. The new thermostats (3 of them--Diversitech PS32H) only work when connected to Unit or P9. However when connected to P1 - P4, the circuits Y1, Y2, Y3, O, W and G are energized the second the wire is connected, even though the thermostat is off.

For example, I verify that the thermostat is off and a reading of 0 volts between C and G. if I connect R, C, and G, The measured voltage between R & C is 25.3 volts, and between C and G is 3 volts??(enough to energize the circuit and turn the fan on). If I turn the fan on at the thermostat, the voltage between C and G changes to 25 volts.

I've removed the wiring out of the equation by using a short 3 ft section.

I'm not sure where this 3 volts is coming from on the circuits that are supposed to be off. Any other measurements you'd need me to take to help troubleshoot this? Thanks.

*all voltage is A/C