A few telltale signs that your thermostat may need to be repaired or replaced include: -No power to the thermostat, even after replacing the batteries our AC or furnace won’t turn on or off -The temperature in the room doesn’t match the thermostat reading -The HVAC unit “short cycles,” meaning it turns off before it completes a full heating or cooling cycle -Your thermostat is 10+ years old If you experience any of these issues, it’s important to call a certified HVAC professional right away. Besides leaving you uncomfortable, malfunctioning thermostats can put undue strain on your HVAC unit, wearing out its components.