Troubleshoot Nest thermostat T error codes during a System Test

CAUTION: It’s important to protect yourself your thermostat and your system. Turn off power to your system and thermostat at the breaker or fuse box before exposing or adjusting any wiring.

1. Pull of the Nest thermostat display.

2. Make sure that your system wires are connected to your thermostat correctly. Use the wiring diagram the Nest app gave you during setup.

• If you don’t have a wiring diagram
  • Refer to the picture of your thermostat wires that you were instructed to take by the Nest app during setup.
  • If you didn’t take a picture or can’t find it, follow these instructions, and take a picture of your system’s wires on the control board. Use this picture to enter the wires into the Nest app
    
    1. Open the Nest app .
    2. Tap Add .
    • If you already have a Nest product in the app, tap Settings in the top right corner of the app home screen. Then select Add product and pick the thermostat model you have to install. 
    • Select Start installation (even if you have already installed your thermostat).
    • Follow the app instructions until you get to the wiring diagram step. Use the picture you took of your system’s control board to enter your thermostat wires into the app.

3. Make sure you’re turned off power to your system at the breaker or fuse box to help prevent damage.

4. Move the wires to different connectors to match the wiring diagram. If you need to move wires, your thermostat will ask you a few questions.

5. If the wires are in the right Nest thermostat connectors:

Check that each wire is fully inserted into its connector and that every connector with a wire is down as shown. Check that each wire has ⅜ inch (6mm) of exposed wire.

 

6. Turn power to your system back on at the breaker or fuse box.

7. Re-test your system. On your thermostat go to Settings>Equipment. Then select Continue and then Test.