Nest thermostat star terminal

A Nest thermostat’s star or O/B terminal can be used to control several different system functions, depending on what type of system you have. For example, you can use the star terminal to connect a wire that controls a humidifier or dehumidifier, or emergency heat.

• During setup, the app will give you a custom wiring diagram to install your Nest thermostat. You should only insert a wire into the thermostat’s star terminal if the wiring diagram tells you to.
• If the app instructs you to connect a wire to the star terminal during setup, the thermostat will prompt you to identify the wire and its function.
• No matter which Nest thermostat you have, you can only put one wire into the star terminal, so only one function is supported at a time.
• If you upgrade to a new thermostat, you'll be asked what equipment is connected to the star terminal. If you're unsure, exit the setup flow and check your previous thermostat's wiring. Go to Devices your device's tile Settings Thermostat Wiring.
  • Optional: To check the wiring from the thermostat, go to Settings Equipment.

Important: If you’ve connected a humidifier, dehumidifier, or multi-speed fan wire to the star terminal, we strongly recommend that you get help from a pro.