Originally Posted By: Formermac
What happens if the batteries are proven to be good?


some brands of thermostat are known to be unreliable

unmount the thermostat from the wall and then connect the two wires going to the furnace or use a jumper

if the furnace activates then the thermostat has failed

the older mercury thermostats were far more reliable than the newer non-mercury ones


Originally Posted By: Formermac
a thermostat is wired to 24 volts DC and the batteries are solely for the benefit of maintaining your preset programs.


incorrect

the 24 volts only runs thru the thermostat to activate the relay in the furnace
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