Hey sinchurichida,
Thank you so much for posting in this community. I’m sorry to know that your Nest Learning Thermostat 3rd Gen is showing an error code E73. Don’t worry; I’m glad to help you.
The error code E73 on your thermostat means the RC terminal isn't receiving power. So here are some recommendations to follow.
- Verify system power: Ensure that the power to your HVAC system is on. If you have two switches, heating and cooling, ensure the power is on for both.
- Inspect the thermostat wiring: Remove the display of your thermostat and check that the wiring system is inserted correctly and firmly in each terminal.
- Check system board connections: Verify that each wire is connected properly to the system board.
For additional information, you can check out this article: Troubleshoot Nest thermostat help codes.
Keep me posted so I can provide you with further assistance.
Best regards,
Daniel
