Error A906 means that the controller is getting too hot.
The way to resolve this issue is to replace the control board.
QuitCarbon is dedicated to getting homes closer to net zero through the installation of new energy-efficient hybrid water heaters. We are not currently equipped to do service or repair visits but we want to be as helpful as possible. Feel free to reach out to us here or for more information, contact the Rheem Hybrid Technical Services Department.
