Rinnai RL94e - inside controller died - is it really needed?

[Stephenson]

Hi All!

Subject tankless installed in 2018 - so may still be under warranty. When I bought house two years ago, I reset to 140°F using dip switch process.

The inside, wired controller (MCC-91-2W) stopped working two days ago (lights went out) - grabbed the manual, did some online reading, secured the gas, secured the power via the mounted switch beside the unit, and pulled the front panel. Reset circuit breakers, checked for anything resembling burns on the pcb, checked for power to the board, and power to the controller. All looked OK.

Turned on gas, turned switch on and heard buzzing, and vibrations inside the unit, but no lights on the controller.

Shut everything back off and checked wiring to the controller at the heater - 12VDC so should be OK that far.

Power off. Reread the installation manual. Disconnected the wiring for the controller where it had been spliced to the controller. Turned power back on, checked for 12VDC at the wiring inside to the controller - 12VDC (actually 11.98VDC).

More reading - hmmm - didn't realize it would operate without a controller. Taped off leads to the controller, and set (tan) dip switch 5 to ON for 140°F. Works fine.

Quick edit - hooked up remote wired display/controller to 12 battery - attempted to cycle with power button - no lights, nothing.

So, questions:
1. Does this mean an inside controller is not needed - ie that the heater will work fine with whatever set point you have selected? (like a tank type heater)
2. Should the red LED on the PCB be flashing or lit? It is not. I would have thought this would allow fault codes to show like on HVACs, dishwashers, etc.
3. Other than setting temp (scenario - parents like hot showers, but keep the temp at 120°F for little kids) is the controller on my RL94e only necessary to show fault codes? Without the controller how would a tech diagnose the faults - have a separate controller and plug in at the heater?
4. Is there a downside if I don't replace the controller (btw - the 91-2 looks to have been superseded by 601-W)?

Thanks in advance ... my first time evaluating a fault on a tankless water heater!

 

[Stephenson]

Confirmed with Rinnai that parts are 5 year, but labor only 1 year. They also confirmed the new controller is the 601 series. They fellow I spoke with did not know if the LED on the main control board inside the heater had the ability to provide fault codes.

I've reset to allow 140°F operation without a controller - setting tan dip switch 5 to On. I also turned dip switch 6 to Off - I had set it to On when I changed the temp to 140°F previously.

Can't decide if I have a need to set the temp lower with a remote controller - I do lose the ability to determine codes without the controller, but if it gets much more complicated I would probably call tech anyway. So, I wrapped 12V leads from unit inside the house and reinstalled the wall controller (now no longer operational).