The E1 code indeed pertains to Gas.
1.Try tapping on the solenoid valve to ensure that it is not stuck. If the gas company has checked the pressure feed already and is in the right column (8-11 inches of water column) then we have to check the screen filter if it is clogged.
2.Unplug the unit and check all the wire connections on the computer board and check the flow meter sensor too.
3.Make sure that the propeller inside of the sensor spins freely and is not obstructed.
4.The flow meter sensor is the main trigger for the unit's operation. It is located inside the water heater. Just detach the front cover by removing the 4 screws.
5.Then, take out the flow meter sensor and check it.