Swapping E thermostat to 3rd Gen - help!

[JohnQ62]

Hi - I have two zone heating/cooling (single fuel, two compressors/two air handlers), installed in a new home.

I have a 3rd Gen thermostat, working fine.  I have an "E" thermostat that occasionally flashes error with "G" wire, then resumes working.

Got a 3rd gen to replace the "E" - wiring is the same as in the 3rd Gen that works fine.  The E had them wired the same way.
When I install the new 3rd gen (where the E was) error says E72 no power.
When I put back the E, works fine.

Any ideas?

[JohnQ62]

Here's the wiring for the E (which was working with an occasional error on G wire (E72)

Y1 - Yellow wire
G - Green

R - Red

W1 - White
C - Blue

Ob - Orange

[zoeuvre]

Hi JohnQ62, 

Uh-oh! I'm sorry to hear that your recently installed Nest Learning Thermostat is giving an E72 no power error. Did you try using the Help Center or troubleshooter before contacting support? If so, which steps have you tried already? And remove the C wire from your Nest Learning Thermostat.

1. Turn off the power to the system at the breaker box.
2. Remove the thermostat display.
3. Remove the wire from the C terminal.
4. Reinstall the display and press it until it clicks into place.
5. Turn the power back on.
6. To verify if the issue is resolved, check if the error code no longer shows on the display and the Nest app or Google Home app confirms that the thermostat is online.

Let us know how it goes.

Best,

Zoe

[JohnQ62]

Thank you - it seems the wiring plate for the 3rd gen is a bit faulty - the Rc tab was not springing up (has no wire in it), so I popped it back up and working fine now.

[zoeuvre]

Hi there, 

Awesome! I'm glad that everything has been sorted out. If you have questions or concerns in the future, feel free to start a new thread, and we'll be happy to help.
 

Regards,

Zoe