Rinnai Persistent Cold Water Sandwich: Firmware upgrade or other troubleshooting?

[ColdWaterSandwich]

The Rinnai shouldn’t shut off if the shower is flowing at least the minimum just because more hot water was called for at another fixture then that demand was satisfied.

Might have brain trouble with the unit if it’s not throwing a trouble code.

I would turn the circulation pump off and isolate it with a stop valve and see if the unit operates correctly under that condition.

Really good suggestion, thanks.

I agree the brain/programming seems to be acting wonky. When I test each function and sensor independently they seem just fine, but the actions the heater take under the flow variation scenario I describe don't make sense.

I need to figure out the best way to add one more isolation valve.