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Rinnai R85e, no power to controller, no hot water
I thought I would share my experience hoping it helps others. I have a 2005 Rinnai R85e instant water heater that went dead between showers. No power to the controller, removing the controller wires from the board didn't help. Confirmed 120VAC to unit, checked continuity of both fuses, confirmed power going to transformer 120VAC and 100VAC on secondary side of the transformer (had to use small wires since my tester was too big but don't let them touch! Or get ready to buy new fuses, how do you think I learned). Once power to the control board is confirmed, unplug everything from the control board (leave the small power supply screwed to the front of the control board plugged in) except for the plug coming from the secondary side of the transformer. If you have power to the board but no power (24 VDC) at the terminals going to the wall mounted controller it's a bad board. I bought a new one from Rinnai through a local dealer for $200 overnight shipped and have hot water again. Make sure to check the 2 DIP switch settings and set the new board to the same settings. Hope this helps someone. Rinnai tech support was outstanding and walked me through the last steps when I hit a diagnosis wall but wasn't ready to sink the $200 yet.