Upon arrival I completed diagnostics and found the stat was showing system in heating mode however no voltage at furnace board. The system did not have common wire. I removed stat and charged with usb: let charge for 20 mins and reinstalled. I restarted the system. The system is again operational. Advised customer once it warmed up to pull stat off and let it charge more. The system is operational and heating upon departure. I recommend replacing stat with eco bee.