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.

 

[ColdWaterSandwich]

I'm very peeved right now. I planned my day around Rinnai's supposed 8 am - 8pm ET customer service times. I got my work done by 5:30 pm ET and made my first call to them; the office is now closed. I'm supposed to call back within office hours of 8am-8pm ET. Uhhh... it's not even 6 yet. The text chat is closed also. There's no chat button now (I had seen it earlier in the day).



Meanwhile, I've been observing various parameters in action while people are using the hot water. Thank gosh for cameras to record this stuff for later review.

Observations:

• The system seems to easily fire up the heat exchanger output from resting to around 190-200F. Problems I'm seeing are not about inability to fire the burner.
• Fairly often low WH output temps seem to be a result of over-mixing cold water into the output. My output set temp is 125F, and my input water temp is around 50F. I've seen the output drop into the 90s or below while the heat exchanger output is 140+
• The worst cold spikes definitely are associated with the flame being turned off after part (not all or even most!) of the hot water demand is eliminated. So, the scenario where the shower is running and someone briefly turns on/off a vanity sink hot water tap. The main problem happens on the "turn off" part of that cycle, because the burner is turned off, but even while the vanity tap is on (and the burner is running), it seems the system frequently (not always) is adding too much cold water, at least at first. HEX output remains high-ish but the WH ouput temp plummets. Then when the flame is shut off, it's massive cold water sandwich time.

I may have to rearrange some work next week to talk to these folks during business hours...

EDIT: PS: How do you clear the trouble code list? I'd like to reset it. Currently just has one Code 11 that's been there for a week or two.

 

[Twowaxhack]

Yea i’d turn that circulator off and valve it off.

Then I’d eat some tacos and drink some beerZ.

Then I’d see if it’s working differently.

Then tacos and more beerZ I’m sure.

 

[ColdWaterSandwich]

Yea i’d turn that circulator off and valve it off.

Then I’d eat some tacos and drink some beerZ.

Then I’d see if it’s working differently.

Then tacos and more beerZ I’m sure.

Sorry forgot to report back on this. I deselected recirculation for a test. Didn't have any effect on my issue. I haven't yet put an isolation valve into the recirc line, but I did test the inline check valve (located right before the recirc meets the cold water inlet line) that prevents water from flowing the wrong way, and it works perfectly, not a drop gets past it. Adding an isolation valve will reduce the amount of flushing of lines I have to do each year after I descale the system, so it will get done sooner or later, but it's not causing my problem. The search continues

Tacos and beer sounds good about now!

 

[Mitchell-DIY-Guy]

Oh, the simplicity of a tank heater…

 

[Twowaxhack]

Oh, the simplicity of a tank heater…

I would’ve had this Rinnai working by now I promise .

He needs to call tech support but they may not entertain his call. They may ask that he calls a qualified service plumber.