I have three floors in my home. The bottom floor has its own gas furnace and the 2nd and 3rd floors share another gas furnace. Everything was working great until I added a NEST to the first and second floors.
The NEST works wonderfully on the first floor (own furnace).
The NEST won't turn the heat on on the second floor (shared furnace.) When I use the Honeywell thermostat on the third floor, the heat turns on just fine.
Can anybody point me in the right direction? Does this sound like a wiring issue? I've ruled out fuses because the heat works fine on the third floor. Is that a terrible assumption?