One thermostat works, the other doesn't
I recently moved into a new apartment. I have one thermostat on the first floor and one thermostat on the second floor. At first, both thermostats worked, but now only the second floor thermostat works. I purchased a new thermostat and installed it on the first floor, but no luck. To make sure I purchased I working thermostat, I installed it on the second floor and it works. I don't know what it could be. Any suggestions??? And how much might this cost to get fixed??? Thanks!!!