Honeywell CT3400 Programming And Installation Instructions page 36

The thermostat's current
setting does not match the
display temperature.
■ Check that the wiring hole in the wall behind the wallplate has
been plugged with insulation to prevent drafts that might
adversely affect thermostat operation.
■ Be aware that it is normal for the current setting and display
temperature to differ occasionally.
33 69-0733B—1