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Thermostat wire undetected or unconfigured

If your thermostat isn’t detecting a wire, or there’s a power issue, you should check that the wire end is straight, fully inserted into the wire connector, and isn't corroded.

Google Nest thermostats detect wires by testing them in two ways: mechanically (is a wire inserted into the connector) and electrically (electrical current on the wire). If a required wire fails either of these tests, you might get a “wires aren’t detected” or similar message, and may not be able to finish setup.

Undetected wire

Strip and fix the wire

  1. Important: Turn power to your system off at the system switch or fuse box. This helps protect your system and thermostat from possible damage.
  2. Pull the thermostat display off the base. 
  3. Pull out one wire and inspect it.
    • The exposed part of the wire should be ⅓ to ½ inch long, clean and straight
    • Cut and re-strip any crooked or corroded wire ends
  4. Re-insert the wire.
    Important: Make sure that the wire connector’s button stays down. If not, the wire isn’t fully inserted, and the thermostat won’t detect it. 
  5. Repeat the above steps with each wire.
  6. Once you've checked all the wires, push the display onto the base until you hear a click.
  7. Turn power to your system back on.

Incompatible wires

Stranded wires

Nest thermostats don’t support stranded wires, they require solid-core copper wires.

If your low voltage wires are stranded (each of the wires is a bundle of smaller wires), reinstall your previous thermostat and contact a local pro to have your thermostat wiring replaced or adapted with solid core wire so it can work with Nest thermostats.

Wires are too small

Your Nest thermostat might not sense your wiring if the wires for your heating and cooling system are too thin. Nest thermostats require wires between 18 and 22 gauge, which is standard for residential heating and cooling systems. Anything smaller than 22-gauge wire could be too thin for a Nest thermostat to detect.

If you aren’t comfortable replacing the low voltage wiring in your system yourself, contact a local pro for help replacing these wires.

Unconfigured wire

You will see this message if your Nest Thermostat detects a wire in a connector, but you didn’t enter it into the app during setup. 
You can also check for unconfigured wires by going to the Equipment menu on your Nest Thermostat. It will show you unconfigured wires in orange. Wires that are recognized by the app will be blue.
To fix an unconfigured wire issue: 

  1. Follow the “Strip and fix the wire” steps at the top of this article for all unconfigured wires.
  2. If the issue isn’t resolved, reset your thermostat. Go to Settings  and then Factory Reset 
  3. Begin thermostat setup with the Home app again. On the main screen, tap Add Add and then Set up a Nest product.
  4. Re-enter all the wires connected to your thermostat. Double check your account for any unconfigured wires.

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