I am trying to install 2 Honeywell RTH7500 programmable thermostats to
control 2 (out of three) separate zones (1st floor & 2nd floor) within
The old thermostat (TrolAtemp) on the 1st floor had 6 wires, R, W, Y,
G, B and O (tan line). The RTH7500 does not have a connection for "O"
for a Conventional (non Heat pump) systems.
After installing the 1st floor, everything worked fine on the 1st floor
but after installing the 2nd floor we found that the 2nd floor
thermostat no longer worked. Also, the thermostat in the basement (not
replaced) stopped working.
I think the "O" controls the other 2 zones (the total system can be
turned on/off only from the 1st floor) but the RTH7500 installation
guide doesn't say what to do.
Can anyone help? Honeywell support is only open M-F 8-5