How to Know if a Home HVAC Thermostat Is Bad

Locate the thermostat and remove the cover from it using a screwdriver, or by pulling it away from the wall gently, depending on your model.

Look inside to locate a battery compartment. If a battery compartment exists, remove the old batteries and replace them with new batteries. Not all HVAC thermostats have battery compartments, since some attach directly to wall wires for power.

Look at the thermostat and slide the power button to the “off” position. Then look for another button labeled “auto” and “fan,” and slide it to the “fan” position. If you have a digital thermostat you may need to push a button, such as "fan" to display other options on the screen. Refer to your thermostat's owner's manual to locate the settings.

Locate the main breaker in the home and shut off power to the thermostat. If you have a battery operated thermostat, simply remove the batteries instead of shutting off the breaker.

Look for the screw terminals that the colored wall wires connect and locate the ones labeled “R” and “W.” Loosen the screw with a screwdriver and unwrap the wires from them. Twist the ends of the two wires together then slide the power button to the “On” position.

Listen carefully for the furnace to turn on or walk to a vent and feel it to see if air comes out. If the HVAC system turns on at all, then it means the thermostat is bad. Turn the system off and purchase and install a new thermostat, or call a HVAC Repair professional to perform the repair.