Before calling service technician, open following link for resources including error codes, Rheem chat and possible manual:http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
Error codes are considered start-point for troubleshooting, and give service technician direction for isolating problem.
Error 82 appears as 'gas type data failure' > 'Program PC board for proper gas type.'
Gas type is choice between LP gas and NG natural gas.
Gas type programming is controlled with dip switch setting.
I do not have service manual for product, and would not suggest changing dip switches without specific information beforehand.