I have a 5 hear old dual zone Heat/AC system with two Honeywell T8001 thermostats. These units don't use a battery.

About once a year one of the T8001s goes blank. Since the T8001 clips to a bracket on the wall, I mobilized my advanced troubleshooting skills and simply swapped the units. The trouble stayed with the thermostat, not the zone. Switched back, same one still dead.

Hmmm. Must be the thermostat. After about a month, I switched them again so I could run the OTHER air conditioner and... both came back on.

This has become an annual ritual. Blank thermostat. Swap thermostats. No good. Switch back. Still no good. Wait about a month. Switch thermostats. Both work fine.

Is there something I can check in the flakey one? Go drastic and buy a new thermostat? Tape chicken foot to it?

At least you have your sense of humor and unfortunetly also a bad stat , I think you will probably have to replace it. Mike

You are supposed to change the subbase for the thermostat when you change them. Honeywell sometimes has different subbases for the same model t stat but they were made in different years. Also some of the subbases has some electronics for the thermostat in it. That can also cause a problem.