Nest Thermostat No Power

[Ericdavids41]

I recently installed a Google Nest Thermostat Cotton White Snow.  It worked great for two days.    It then went offline with error codes of no power (E298 and M20).  Batteries in thermostat are brand new.  C wire is installed.   Circuit breakers are all on.  Has anyone experienced a similar issue?  Is this a sign of a bad thermostat or an AC issue?   

[CoolingWizard]

@Ericdavids41 , you need to use a Volt Ohm Multimeter and verify the Alternating Current between your R wire and your C wire.  You should measure 24VAC +/- 5 volts.  This error is common power not present. 

AC Cooling Wizard