HVAC Thermostat Diagnostic & Repair Guide: How To Fix a Thermostat

Symptom	Check Click on underlined items for further information
Heater or A/C won't turn on	Check for a blown fuse or tripped circuit breaker Make sure thermostat is actually set to "heat" or "cool" Replace the battery in the thermostat If one will turn on but not the other, troubleshoot that equipment
Thermostat doesn't come on at the right temperature	Mechanical thermostats need to be level to operate correctly, make sure it is level Double check that it is programmed correctly Replace the battery
Thermostat won't retain programmed settings	Replace the battery