It's a model TH5110D.

I replaced the batteries and the problems started. Figured it was the thermostat so reset it by reversing the batteries but still just clicking. I also checked the breakers and replaced the filters. Any ideas?

Check the fuse in the thermostat. Check the fuses on the air handler in the attic. Check the float switch on the pan in the attic. Depending on the model there may be a reset switch on the condensing unit outside.

Thank you. Will do.

Squirrel chewed a wire. All good now.

Sounds like a good excuse to to buy a .22 cal air rifle and pop some tree rats.

I'm having the same issue. Thermostat is calling for heat but neither furnace or blower are on. Checked breakers and switches. Don't see any evidence of rodent chewing wires.

Any ideas?

ETA mine is an ecobee

Had the same with Nest. I had to call Nest and re-install with slightly different wiring. Funny thing is that it worked for 2 years before I had an issue. Worked fine ever since.

Something about there wasn't enough power to trip the solenoid. And for the record, called an AC company first.

Update:

Cut power to it for awhile. Still couldn't find anything out of the ordinary at least to my untrained eye. Turned power back on. This time when the thermostat called for heat the furnace came on but the fan still didn't. Didn't like the idea of just heating the attic so I turned the heater off at the thermostat. Guess I'll be calling someone tomorrow…