C Wire not detected on Nest Learning Thermostat.

[Ken000]

Not connected to C wire. My learning nest thermostat aren’t detecting C wire. Resulting in E79 no power to C wire, even though I did check the C wire and it got electricity and the voltage around 24vac. I really need some help and much appreciated if someone could give some advice.

Thanks

[Jenelyn_O]

Hi Ken000,

Thanks for reaching out. If your Nest 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).

Check out the guide below:

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. Once you've checked the wire, push the display onto the base until you hear a click.
6. Turn power to your system back on.

Let me know how it goes.

Best,

Jenelyn