On Feb 11, 10:50 am, "Mr. R" wrote:
I had a Honeywell digital thermostat in a good interior wall location. It
seemed to behave well except when it was really cold outside. When that
happened, my setting of 68 would invariably go to 72, and sometime more.
Thinking that the thermostat was defective, I bought a new one and it still
continues. Can anyone advise why the thermostat won't cut out the furnace
when the setting temperature has been reached ... only when it's extremely
cold outside?

Just a thought, but are you sure nobody else in the house may have
bumped the temperature up? Ours is set to 68, but on a cold weekend
I'll bump it up to 70 using the temporary setting. The program will
still show a setting of 68 because I did not re-program it, but used
the temporary setting to increase the temperature.

-Felder