Here are some of the most common causes of these errors and how to fix them. For help with specific wiring errors, the troubleshooting tool widget will guide you through detailed troubleshooting steps.

Wires aren’t fully inserted

Make sure the copper part of the wire is fully inserted in each of the connectors. The ends of the wires need to be straight and they need between ⅓ and ½ inch of exposed wire for a reliable connection.

Stranded wires

If your low voltage wires are stranded (each of the low voltage wires is made up of lots of smaller wires), you may run into this error because the strands of the wire have flattened out, so Nest thinks there is no wire inserted into the connector.

Follow these steps to resolve the issue:

• Turn off the power to your heating and cooling system.
• Remove the Nest display to access the wiring.
• Remove one of the installed wires.
• Twist the tip of the wire so that the individual stranded wires that make up the wire are tightly bound together.
• Reinsert the wire into the same connector.
• Repeat the same process for each wire connected to the Nest base.
• Replace the Nest display.
• Turn the power back on to your heating and cooling system.

If this fixes the issue, Nest will notify you that the detected wiring has changed. Go ahead and finish setting up Nest.

Wires are too small

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

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