Just a heads up, many of us have changed out the basement thermostat to the Honeywell digital version to control the heat in the basement. My batteries needed changed, and I removed it from the mounting plate, changed the batteries, and tried to re-install it back, and it would not connect.
Inspecting the thermostat, all 3 pins on the back pulled loose from the circuit board. New one on order. Inspect your pins when changing batteries, and if it is working now, leave it until it warms up...lol.
This is an old image - wish it was 76 now.