topic Re: Upgrading From 2nd Gen to 4th Gen - Wiring in Nest Thermostats

Upgrading From 2nd Gen to 4th Gen - Wiring

OsideNickG — Sat, 10 May 2025 15:02:04 GMT

Hi,

If I am upgrading from the 2nd Gen to 4th Gen would I just mimic the wiring exactly as it is?

I have a dual fuel heat pump set up with the 2nd gen if that matters.

I can add pictures of the existing wiring but I thought maybe this is a simple question.

Thanks,

Nick

Re: Upgrading From 2nd Gen to 4th Gen - Wiring

JM14 — Mon, 12 May 2025 03:04:18 GMT

I recently upgraded from an earlier generation a couple of days ago and found that the videos etc. found on this page:

https://support.google.com/googlenest/answer/10125150?sjid=11924827530077377873-NC#zippy=%2Csteps-to-install-your-thermostat

made it really easy to understand. Hope this helps. Good luck with the installation!

Re: Upgrading From 2nd Gen to 4th Gen - Wiring

humbertogarcia — Tue, 13 May 2025 17:23:36 GMT

Hi OsideNickG,

Thanks for posting in the community! I'll gladly check on the wiring compatibility for you between your Nest Learning Thermostat (2nd. gen) and the Nest Learning Thermostat (4th gen).

@JM14 Thank you for referencing the help article: Get started with your Nest Thermostat and Nest Learning Thermostat (4th gen).

To best address your concern, could you please provide me your country of residence and a picture of the current wiring setup, including wire labels?

Please remember to turn off the circuit breakers for your thermostat before taking any pictures.

I look forward to your response and am here to assist you further.

Regards,

Humberto

Re: Upgrading From 2nd Gen to 4th Gen - Wiring

OsideNickG — Tue, 13 May 2025 17:03:19 GMT

Hi Humberto,

I live in the US, here is the existing wiring and diagram, I replicated it and I think it is working as expected.

Re: Upgrading From 2nd Gen to 4th Gen - Wiring

humbertogarcia — Tue, 13 May 2025 17:39:41 GMT

Hi OsideNickG,

Thanks for sending your wiring details and the diagram!

That's great news that it works right! And yes, the Compatibility Checker link will give you that final confirmation.

Let me know if any other questions arise or if you need anything else at all. Happy to help!

Regards,

Humberto

Re: Upgrading From 2nd Gen to 4th Gen - Wiring

OsideNickG — Tue, 13 May 2025 17:50:18 GMT

I had to make a choice for the OB wire and it recommended O, how do I know for sure it worked?

I did a heat call and it worked as expected, I have it set to alt heat so I can use natural gas instead of the heat pump right now.

I guess one more test would be to turn off the alt heat setting and make sure the heat pump works right?

Re: Upgrading From 2nd Gen to 4th Gen - Wiring

humbertogarcia — Tue, 13 May 2025 21:27:33 GMT

Hi OsideNickG,

Thanks for sharing the willingness to further troubleshoot, You're correct; an additional test will confirm that the wiring is correct.

How to Perform the Test:

Access Thermostat Settings: On your Nest Learning Thermostat (4th gen), navigate to the settings menu. This is usually done by pressing the thermostat ring or tapping the screen and then selecting the "Settings" icon.
Locate Heat Settings: Look for options related to "Heat," "Heating," or "System Mode."
Turn Off Alternative Heat: Find the "Alt Heat," "Auxiliary Heat," or a similarly named setting and disable or turn it off. This will force the thermostat to rely on the heat pump for heating.
Initiate a Heat Call: Set the target temperature on your Nest a few degrees above the current room temperature to trigger a heat call.
Observe:
Listen for the heat pump to turn on. This might sound different from your natural gas furnace.
Feel if warm air is being circulated through your vents after a few minutes.
Monitor: Allow the heat pump to run for a sufficient period to ensure it's heating effectively and maintaining the set temperature.

Feel free to share the results with me, I'm glad to assist you.

Regards,

Humberto

Re: Upgrading From 2nd Gen to 4th Gen - Wiring

OsideNickG — Thu, 29 May 2025 18:57:54 GMT

sorry for the late reply, I haven't done the test but I did initiate a cooling session and realized that the heat pump turned on. I googled it and the suggestion was to change the choice for the OB wire, I did this and then the cooling worked as expected. I assume I should still run through this test anyway though?

Re: Upgrading From 2nd Gen to 4th Gen - Wiring

humbertogarcia — Thu, 29 May 2025 19:46:47 GMT

Hi OsideNickG,

Thanks for the update. I'm happy to hear your proactive adjustment to the OB wire setting resolved the cooling issue and your heat pump is now working as expected. That's fantastic.

You've essentially run a successful real-world test. While it seems perfect, going through the suggested diagnostic steps would offer a quick final confirmation.

Feel free to post if you complete those steps or need any additional help.

Regards.

Humberto