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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Maybe, have a Nest thermostat suddenly display a E73 code

Customer Question

Maybe, have a Nest thermostat suddenly display a E73 code indicating no power.
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: No clue, everything had been working until a few hours ago. How do I determine whether it is a thermostat v. furnace issue?
JA: Do you plan on doing the work yourself?
Customer: Hard to know without having any idea the extent of the issue
JA: Anything else we should know to help you best?
Customer: No, everything I know at this point;
Submitted: 9 months ago.
Category: HVAC
Expert:  airheatman replied 9 months ago.

E73 or E23?

Customer: replied 9 months ago.
E73, no power (Rc). May have a temporary solution from Nest. They had me disconnect the A/C wire, enables me to turn on the heat.
Expert:  airheatman replied 9 months ago.

Do you have a volt meter to see if we have 24v between RC and C?