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.

 

[ColdWaterSandwich]

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.

It's quite possible they will point me to a service guy. I know the plumbing company they will refer me to (there's only one on their list in my area) and while they are not an "avoid at all costs" company here, they don't have a great reputation. It's possible or likely that the fix is outside my comfort zone, but I want to make sure the diagnostics are sound before I pay someone for a repair if one is needed.

To that end, the only thing I can think of that I have not done so far is test the pressures in the unit; I've got a manometer ordered for delivery in the morning. But, I'm now having trouble finding out where to hook it up to test. I just went through the installation manual with a fine toothed comb and didn't see it.

Anybody got a link to the service manual for the RUR199iN? Or a good video showing where to hook up the manometer and the steps? I've found a document for a different model (RC80H series) that gives good detail even I could follow, including the expected pressures under forced low and forced high burn conditions. But maybe the RUR199 is a bit different. I don't even remember seeing the DIP switch referenced on the RC series ;-) but I will take the cover off tomorrow and poke around.

I'm more technical than most homeowners (a decade supporting industrial robotics) but I make no claim to plumbing expertise.

 

[Twowaxhack]

There are two places to connect a manometer. There’s a screw on the gas inlet. Remove the screw and push a hose over where the screw was.

Inside the unit on the gas manifold there’s another screw. Same deal as above.

You shouldn’t mess with the inside port unless rinnai is advising you on what to be checking for.

 

[ColdWaterSandwich]

There are two places to connect a manometer. There’s a screw on the gas inlet. Remove the screw and push a hose over where the screw was.

Inside the unit on the gas manifold there’s another screw. Same deal as above.

You shouldn’t mess with the inside port unless rinnai is advising you on what to be checking for.

Thanks. I probably should have looked under the unit for the big inlet port with the red tape next to it marked GAS and the obvious screw on a nipple.

So, I've got plenty of gas pressure.

Static pressure with nothing in the house using more than a pilot light amount is a steady 7.3-7.4 inches of water column. If the furnace is running full boar, it drops to about 6.8" (surprising; I had thought the furnace would eat more gas).

With just the Rinnai running (no furnace), with a light load such as slugging water through the recirc lines, it's down to about 6.9-7."0. With a heavy load of about 3 GPM from the hot taps (it's rare I would draw more than this), pressure drops to about 6.15".

Furnace heating plus heavy load of hot water flow takes me down to no lower than 5.2"; I left the water heater and furnace on together for a while and saw the pressure go up and down a bit (variance of about .2 to .3). But never lower than 5.2.

Spec for the unit is 3.5" - 10.5" natural gas, so there's no condition I'm running that would even get close to the lower limit. So, good news is I don't need expensive pipe rework (and, if a service guy tries to sell me pipes, I can send him packing). Bad news I still don't have an obvious culprit.

I appreciate the help. The Rinnai folks will likely have me check enough gas at the burner in case any regulator adjustments are needed in the unit; I see the plug on the case that's removable to access that, I think. But there's nothing for me to poke at meantime.

 

[Twowaxhack]

What doesn’t make sense is why the unit isn’t throwing a trouble code. Makes me think the brain is bad or is at least on some type of illegal drugs.