Diagnosed no power to the nest thermostat Diagnose loud booming noise in flame roll out at startup No power to the thermostat was caused by a faulty blower motor causing the primary limit to shut down during overheating and result no power to the thermostat went overheated Booming noise and roll out is caused by a failed pressure regulator in the gas valve. Slow opening gas valve is dumping 4.9"wc full volume at startup and running at 4.5 but cannot be adjusted. Install diversitech brand 1/2 horsepower indoor blower motor Install OEM Armstrong Air intermittent pilot spark ignition gas valve (White-Rodgers retrofit) Test run heat mode at 138 and confirm temperature rise is within the 55 to 85 furnace specs Blower high speed set to heating medium high set to cooling