I'm afraid I didn't follow this thread that closely but did anyone mention making sure any holes in the wall behind the T-stat were sealed? That would be the first thing I always look for. I've found that even the tiniest holes can let in enough air to screw with an electronic sensor. Even air getting past/through the little plastic anchors for the mounting screws. o_O
TDD
In my case that is covered too, the thermostat is mounted to a paneling wall of the closet that the furnace is in, the walls are bare studs inside the closet, and the furnace is direct return instead of ducted with 2 20x25 filters in an A frame shape on top (it is a downflow), IE the area behind the thermostat is conditioned space.
Cool! No pun intended. ^_^
TDD
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