We full time and long ago stopped messing with air pocket in the water heater. As far as the electric not working, did you press the reset buttons to see if that solved the problem? If that doesn't work, is the 120 volt breaker tripped? There may be a relay that has failed, but that involves removing the water heater to fix that. The electric element could have also failed, but the volt meter is needed for that. The gas mode is at least working if the water got hot enough to expand to push water out of the pressure relief valve, but possibly the thermostat on the gas side has weakened, needing replacement. Good luck getting hot water working again.
Bob & Becky
2012 Chevy 2500HD D/A CC 4WD