I'm having issues with my Honeywell RTH7600D thermostat. It's a couple of years old and has worked fine until recently.
We're in Southern California and the cold weather has recently started so I went to check the thermostat. The display was blank and the batteries were dead, so I replaced them. This brought the thermostat "back to life", except for one thing: it does not display the current temperature anymore. The LCD display simply shows two dashes where the temperature should be. I can turn on the fan, and it starts blowing, but I cannot set the target temperature or turn on the heater.
We do not have an air conditioner, just a gas heater. I have cycled the power on the heater and on the thermostat (by disconnecting it and removing batteries), without success.
I have researched this issue online, but the only results I get from googling are pages that address a completely blank display on the thermostat (by replacing the batteries). This is not really the issue I'm having - I can work the controls and turn the fan on/off.
It looks to me like either a faulty thermostat, a failed (or failing) connection between the thermostat and the temperature sensor, or a furnace problem.
Can anyone suggest additional steps to troubleshoot this problem?