Nest 3rd Gen has power but won’t start furnace

[Jasoncpslo]

I suspect the wiring circuit board is to blame and am looking for help to confirm and determine what to do. Can I replace the wiring circuit board or do I need to purchase a full replacement?

Note: I have two furnaces in the house so I have two Nest’s that comes in handy as I troubleshoot. I noticed the Google logo on the screen and flashing green light. Once the logo disappeared I could not turn on the screen to see anything. I did all of the following and concluded the wiring circuit board must be the issue:

1. Removed the nest and plugged into the micro USB to charge in case it’s a power issue. The screen eventually directed me to reattach and I noticed the power exceeded 3.8v. The screen comes back to life but the heat won’t come on when the Nest signals to the furnace.
2. Ran the Heat test from Equipment >Continue>Test>Heating. No luck
3. Held down the Nest button for 10 seconds to restart while it’s plugged into the wall. No luck
4. Reset the Nest in Reset>Restart while it’s plugged into the wall. No luck
5. Flipped the furnace power off for 30 seconds and on at the breaker. No luck
6. Flipped breaker off, removed Nest, connected the Rc and W wires to bypass the Nest, and flipped breaker on. FURNACE TURNS ON AND HEATS THE HOUSE. So there’s power to the wiring circuit board and the furnace works.
7. Reattached the wiring correctly and attached the Nest. Same symptoms - Nest isn’t starting the heat in test mode or changing the temps to trigger the heat. Green light continues to flash in all circumstances
8. Switched the Rc wire to the Rh plug hoping that terminal would work. No luck.
9. Grabbed the second Nest (which works fine) in my house and attached it to this wiring baseplate. Same symptoms as the other Nest!

Did I miss anything? I’m hoping there’s an option to only replace the wiring baseplate. Thanks

[Markjosephp]

Hello Jasoncpslo,

Thank you for taking the time to let us know about your inquiry. I understand the frustration you're experiencing with your Nest Thermostat and the heating issue. Based on your thorough troubleshooting, it does seem like the wiring circuit board could be the culprit. Your detailed steps to test and rule out various possibilities are commendable.

Considering the symptoms persist even when using a known-working Nest Thermostat, it strengthens the case for a potential issue with the wiring baseplate. Before making any decisions, there are a few additional steps you can take to further narrow down the problem:

• Ensure all connections on the wiring baseplate are secure. Sometimes, a loose wire connection can lead to intermittent issues.
• Examine the wires for any signs of wear, damage, or fraying. Damaged wires can cause disruptions in the system.
• Gather the power readouts in the Technical Info settings.
• Try activating your cooling and fan to see if it works.

Let us know how it goes.

Best regards,
Mark

[Jasoncpslo]

Mark,

I finally got the chance to follow up with your recommendations and the Nest is still not working for cooling, heating, or fan testing. I pulled the baseplate off and removed and reinstalled all wiring. And by the way, the wiring was new about two years ago when we renovated. The Neat was working fine before and after the renovation. 

[Markjosephp]

Hi there,

I appreciate your diligence in troubleshooting the thermostat. Since you've already pulled off the baseplate and reinstalled the wiring, and considering that the wiring is relatively new, it's perplexing that the Nest is not functioning for cooling, heating, or fan testing.

To further assist you, could you provide additional details about any messages in the Equipment settings or specific behaviors you observe when attempting to try the steps? Does it have a C wire? Also, have you checked the power readouts in the Technical Info settings?

Keep me posted.

Thanks,
Mark