I am a plumber and we do 2 to 300 new houses a month. We primarily intall 2 brands of tankless water heaters, Rheem and Rinnai. Often these heaters are installed either on outside wall or up in attic and we then run a low voltage unshielded thermostat wire to a controller usually located in master closet. With the Rheems the terminals to connect controller are located at bottom of heater and incased in a plastic piece. From there plug directly into pcb board. When running 2 heaters we will also connect units with a communication link making one unit the master. With the Rheems each end of communication link connects directly to pcb board. The Rinnais are the same with 2 subtle differences. The controller terminals are located at the pcb board and only one end of the communicatiin link connects to pcb board, the other end plugs into a wired plug connector, which this unit is the master. We have no issues with the Rinnais. However the Rheems we are constantly dealing with a code 76 and occasionally a code 82. Code 76 means the unit and controller are having issues communicating. 82 means the chip on pcb board has malfunctioned. To remedy both problems usually means moving controller next to the heaters. I know unshielded electrical lines in house create a magnetic field that can cause interference issues on low voltage line. My question is why do we not have this issue with the Rinnais? Rheem has been no help, but is it possible that the terminals and the wired plug connection inside the Rinnais are grounded? Would grounding terminals on Rheems solve code 76. Code 82 not sure how to ground since both ends of link connect directly to pcb board.