I have a EWC-ST-2D Ultra Zone Controller that originally had mercury thermostats. I replaced both Thermostats with RTH2300 series (Home Depot). In the thermostat instructions, they state if you have an orange and blue wire, then connect the O-wire and leave the B-wire open.
Since the installation, I no longer have heat to Zone 2 however the AC works in Zone 2 in the summer. I download from this website the tech manual. I measured the voltage between C-W, C-Y,C-R for Zone 2 on the control and there is no voltage.
I am not sure if this is caused by the Honeywell RTH2300 series thermostat due to a B-wire that is open? or if Zone 2 is fried on EWC-ST-2D and how I can confirm that. And what I need to do next. Thanks.