The furnace thermostat controls the room temperature in your home. When it does not function properly, the furnace will not operate efficiently. Before you call a repairman, learn how to troubleshoot a furnace thermostat. Many small things can cause a thermostat to operate incorrectly. Sometimes a little troubleshooting will uncover a simple remedy.
Check the main circuit breaker to the furnace to make sure it has not tripped. Sometimes the breaker will trip or cut off when there has been a power surge. If it has tripped you need to reset it. In the event it has not tripped, turn the power off before working on the thermostat.
Place a torpedo level on the thermostat to make sure that the unit is level. This is because the mercury switch will not operate properly if the thermostat is out of level.
Remove the cover of the thermostat, and make sure that the components are not dirty. Spray a couple of bursts of canned air indirectly over the thermostat components to remove any dust.
Inspect for loose or broken wires inside the thermostat. Although it is rare, sometimes the bare end that is connected to a terminal may become brittle and break off. Repair any loose or broken connections using a screwdriver and a pair of wire strippers.
Change the battery if your thermostat is equipped with one. Most LED thermostats are powered by a battery.
Inspect the thermostat anticipator if the furnace is running too long or not long enough. The anticipator is a disc located inside the thermostat and has the word "longer" stamped on it. It can be turned with your finger in one direction or the other. When adjusting, only move it one calibration point at a time.
Inspect behind the thermostat mounting plate. If there is a hole where the wires come through the wall, it could cause a draft which will make the thermostat read an incorrect room temperature. A simple fix to this is to stuff a piece of insulation into the hole.