Hi rgalloway,
Thanks for reaching out — I'd love to help.
The E73 code is for no power to RC wire. In this case, the wire might not be properly grounded, it isn't fully inserted, the wire doesn't have power getting from the control board or the thermostat terminal is defective.
Can you try the steps in this guide: (Note: Turn off the breaker first before touching the wires.)
- Remove your red wire then, strip and cut it before putting it back to its terminal.
- After that, make sure to turn the breaker back on.
- If you have a voltmeter you can use it to check if there's power to your red wire.
- If the issue persists, try to move the red wire from RC terminal to RH.
- Also, could you please provide the photo of your old thermostat wiring?
Please let me know how it goes.
Best,
Jenelyn
