C Wire Not Detecting Suddenly

[mt130]

I have had a nest thermostat hooked up for a few months with no issues. A few days ago I got an alert that the c wire was not detected. I reset the system to troubleshoot and it was not detecting the c wire at all. My system has batteries but also needs the c wire for constant power. Tips before calling someone? 

[Patrick_Caezza]

@mt130 

Is the HVAC system working?

It sounds like there is no power to the HVAC.

Check the breaker, the fuse on the control board, and the safety switches (drain, filter, door).