Dead Battery

[E78Battery]

I have spent money to find out that the battery in my Nest Thermostat and there is no number so that I can speak with customer service. If anyone knows a working number please get it to me bc they will be replacing this Thermostat or battery.

[E78Battery]

Btw it E74

[Patrick_Caezza]

@E78Battery 

The E74 error code means the thermostat is not seeing power on the Rh wire. If you have a voltage meter, you can check the voltage by measuring between the Rh (red) wire and the C wire if the C wiring is installed. If you don't have a C wire, you can measure between the Rh and either the Y , W, or G, wires. You are looking for 24 VAC.

You can also connect the Rh abd G wires together and the blower should turn on.

If none of these work, then the problem is with the HVAC unit and not the thermostat.

[E78Battery]

I had spent money to find out that the battery to my Nest Thermostat is dead and there is no number so that I can speak with customer service. If anyone knows a working number please get it to me bc they will be replacing this Thermostat or battery.