Hello again, there is only a 50% chance that the thermostat is the problem, the other 50% is that the printed circuit card in the furnace blower
compartment is the problem.
We cannot find out which until it fails again, the hope that it stays failed while we do a few tests... that of course is problematical. Intermittent problems are like that.
The problem with changing parts, regardless of what the sales man says or the box says 'easy replacement fits all systems' the huge installation manual tends to be-lie that.
If you do change the thermostat get the very same exact model then change it wire for wire, one wire at a time with the furnace unplugged...then it must be programmed per the 85 pages of instructions.
I would be inclined to wait and see what develops.
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