Walter R. wrote:
We hate this Honeywell T-stat: When it comes on in the morning, the
temperature at the t-stat rises much more quickly than the room
temperature. Because the thermostat is usually 4 degrees ahead of the
room temperature it shuts the furnace off too quickly. The actual
room temp may be 70 but the t-stat reads 74. Since the t-stat was set
to shut off at 74, the furnace stops, although the room temp is only
70. It then keeps cycling on/off and high/low until it reaches 74
degrees 2 hours later.

Either warm air is blowing on the thermostat or there is warmed air
leaking into it from behind the wall.