e2 is not shown among common error codes:
Error e2 might be
: Brownout condition or too low of voltage to thermostat. Double check wiring and check for 24 vac between R and C. E2 will clear 15 sec after proper voltage is restored.
Before calling service technician, open following link for Rheem troubleshoot resources including Rheem chat and typical generic manuals and common error codes:http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
Model number and serial number are required for Rheem contact, and then they tell you what error code means without saying how to fix it, and then tell you to call service technician.
Tankless water heater manuals each say to have qualified technician perform yearly service. Most causes for common error codes are covered by yearly service.
Yearly service is fairly standard in the HVAC and water heater industry with advancement of high-tech 'energy' saving appliances. Of course all costs are energy, and the service call probably costs more that the 'energy' saved by energy-saving appliance. But with high tech stuff like tankless, it is good to have a reliable service guy who knows your machine.http://waterheatertimer.org/images/Tankless-wiring-1200.jpg