The method of fixing a furnace thermostat depends on the thermostat problem. Common thermostat problems include unit start-up failure, mismatch between the thermostat setting and the room temperature, unit turn-off failure, and turning the unit on and off.
To fix a start-up failure, check the power connection to the unit, and replace any blown fuse and dead batteries. If the failure is caused by a tripped circuit breaker, switch on the breaker. If the appliance fails to run, switch off the breaker and check the thermostat for dirt. Remove the thermostat battery and cover. Gently clean the thermostat with a soft, clean brush to remove all dirt and debris that clog the electrical and mechanical system of the unit. If necessary, tighten any loose terminal screws to properly secure the terminal wires, then replace the battery and cover.
A mismatch between the thermostat setting and room temperature may be due to dirt inside the thermostat, improper thermostat installation, poor thermostat location or incorrect anticipator setting. To fix this, clean the inside of the thermostat, reinstall it properly or relocate the unit to a proper location that is free of harmful elements such as cold, direct sunlight and draft. Reset the anticipator if needed.
Dirt, poor anticipator adjustment and unleveled thermostat may cause the unit to constantly turn on and off or hinder its turn-off. To fix these, clean the thermostat, reset the anticipator or adjust the thermostat respectively. Replace the thermostat if all the fixes fail to work.