No Display but App works

[dbstx]

Purchased Nest Learning Thermostat 4th gen in late April 2025 to run my hot air furnace.  It functioned as expected for about a month and then seemed to run out of power with no display.  I tried to charge it, but nothing happened.  Since the heating season was over, I decided to revisit the issue in the fall.  Our plumber just installed a C-wire thinking the Nest wasn’t getting enough power.  When he connected the C-wire, the light on the base went out.  The Google Home app appears to be able to control the furnace but there is no display on the Nest.  How do I get the display back?

[sicsacol]

Hi @dbstx,

Thanks for reaching out to the community. I understand your Nest Learning Thermostat (4th gen) ran out of power with no display while it was connected to your hot-air furnace. I know how concerning this must be, especially since a plumber installed a C-wire to resolve a power issue, and now the light on the base has gone out, even though you can still control the furnace through the Google Home app. I appreciate the detailed information you've shared and the troubleshooting steps you've already taken. No worries, let's work together to get this resolved. To help with that, I have a few questions for you:

• Did you experience any power outages recently?
• Are all the wires of your Nest Thermostat seated firmly in its terminals (with no loose or exposed wires)?
• Was there a light on the base before the C-wire was installed, and if so, what color was it?
• Are there any error codes in the Google Home app?

Any additional details you can provide will be helpful.

Cheers,
Jonathan