nest gen 4 error code e402

[ehs1331]

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Subject: Nest Gen 4 Thermostat – E402 Error

Hello,

I’ve reviewed every post I could find on this issue but haven’t found a solution. I’m receiving an E402 error after being forced to upgrade to the Gen 4 thermostat.

For context:

• My Gen 2 thermostat worked perfectly for years. But was force to buy a Gen4.
• I installed the Gen 4 thermostat using the exact same wiring setup as the Gen 2.
• After installation, the app reports that RC and RH have no voltage, even though both measure 24 volts and the level bubble is lit.
• All other terminals pass in the app.
• I have an all-in-one unit outside.
• If I reinstall my old Nest, it still works without issue.
• I’ve checked the wiring multiple times and everything appears correct.
• I attempted to upload a photo of my wiring but couldn’t figure out how to do so. It says i do not have permission.

Any guidance on resolving this error would be greatly appreciated.

Thank you,
Eric Stevenson

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[EduardoN]

Hi @ehs1331,

Thank you very much for contacting this community! I understand that the E402 error has recently appeared on your Nest Learning Thermostat (4th gen), and that this occurred after a thermostat upgrade because you previously had the Nest Learning Thermostat (2nd gen). After reviewing the troubleshooting steps you've already taken, which I appreciate you taking, it caught my attention that you reinstalled your old thermostat and it is working perfectly. For this, the team would like to learn more about this behavior. When you get a chance, please fill out this form and let us know when you’re finished. We’ll have someone reach out to you via email from there.

Before you complete the form, I would like you to perform a factory reset on this Nest Learning Thermostat (4th gen).

Best regards,
Eduardo