HVAC: Troubleshooting a Bad Thermostat

Temperature and Settings

• The most obvious, often overlooked factor involves the settings on the thermostat. This is the first thing a repair technician will check, and if it is something as simple as a switch in the wrong position, you are likely to still be out a service call fee. Make sure your thermostat is set to the "auto" or "on" position. Switching it to "off" will disable it, and your HVAC system will not work. Also, be sure you have the temperature set at a temperature that is higher than the room temperature for heat, or lower than the room temperature for cooling -- depending on the season. Otherwise, the system will not come on when needed. Also, check the "cool" or "heat" setting to make sure you have the appropriate setting for the time of the year.

Power Supply

• If your thermostat is not getting power, then it will obviously not be able to function. Most of the modern thermostats on central air systems are electronic and have an LED readout on the front. If this panel is blank, it may indicate no power. Check to make sure fresh batteries are in the thermostat if required, and if it is wired directly to your home's power, then check the circuit breaker box to ensure the switch hasn't been tripped.

Wiring

• Your thermostat is the device that allows you to control your HVAC system with ease. To accomplish this task, it has to be connected to the furnace or central unit so it can tell the system what to do. Check the wires going into the wall behind the thermostat for damage or disconnection. If you need to repair or reconnect a wire, you should cut off the power to the system and complete the task. If you are unfamiliar with wiring, call a professional to be safe.

Location

• Sometimes, your thermostat might not be working properly, and the location of your thermostat may be the problem. If your thermostat is located where the sun shines directly on it, at least during part of the day, then it will get a false temperature reading and, during the summer, will turn on too often because it perceives the house temperature to be high. The opposite may happen during the winter if the thermostat is placed directly above a heating vent.

Mercury Type

• If you have an older air conditioning and heating thermostat that is controlled by a mercury-based sensor, then another simple problem could prevent the system from working correctly. If the thermostat is not level, then the mercury will not reflect the actual temperature correctly, and will therefore keep the HVAC from properly heating and cooling.