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.

 

[ColdWaterSandwich]

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.

What I keep coming back to is that it seems to be over-mixing cold water in, but only during times where the flow is not constant.

When the system reports the bypass valve %, is it reporting the commanded percentage, or the actual measured percentage (by referencing some valve position sensor)?

Today and tomorrow are busy days 8-5 ET for me, but Wednesday afternoon may have a window of opportunity to call Rinnai.

 

[ColdWaterSandwich]

So, yesterday I finally called Rinnai. But all their consumer-level support is now web only, and all they did via the online chat was give me a case number and refer me to a list of local Rinnai-approved licensed plumbers. This sucks. I bought Rinnai because they used to be willing to talk to guys like me.

On the bright side, they confirmed that some components like the heat exchanger are still under warranty.

Several of the plumbing companies they referred me to are on the "cold day in hell before I call them" list, as they have bought out older firms where the main guy retired, and they do business sending rookies out to sell unneeded new crap instead of properly diagnosing and fixing stuff.

Still, one name on the list was someone that gets generally good reviews and I've actually had a good exchange with them in the past, so I called and made an appointment for next Thursday. I told the pleasant person answering the phone that the issue was probably something diagnostics intensive, so I was quite happy to wait for the right guy that likes digging into it. I told her I had already checked for a birds nest in the vent pipe; got a laugh out of her.

We will see how it goes. For me, my reluctance to use is plumber instead of myself is more about gaining personal satisfaction in fixing something than the money (I respect and value and don't mind paying for experience). I will post back when there is news.

 

[Twowaxhack]

I had the same problem with a professional home burglary alarm panel manufacturer. They said that tech support was only for installers.

So I invented a company and called them back the next day.

 

[ColdWaterSandwich]

Hi guys, it's been a busy week but I was fortunate to have the plumber come and do diagnostics on my Rinnai. I'm glad with the guy I picked; he clearly works with a lot of these and knows his stuff. I walked him through the symptoms and what I had already looked into.

• He validated that the installation was fine, air and gas were fine, flame looks fine, configuration settings are fine. No sign of recirc inline check valve letting water flow backwards. No sign of any motherboard faults and he says he almost never sees motherboard problems; it's always the other components.
• He felt the system was struggling to come up to proper output temperature under normal shower-level load
• The system eventually does come up to full temp but surprisingly slowly despite hot water being produced in the heat exchanger
• The system showed the same quirks to him that it does in practical use for me, most notably that when a small extra flow like a vanity sink starts, the output temp drops too much, then when the vanity load stops, the flame shuts off and temp plummets
• The problem is real; the degree of variation in output temperature is way worse than normal
• A big AHA! was when I mentioned the heat exchanger output routinely gets up over 190F; he thought this was ridiculous as he is used to seeing the HEX temp only 20-30F higher than the output set temperature

We went through a lot of cycles and he listened for valve openings/closings while watching the various readings. As expected, he believes one or both of the valves (flow control or by pass flow control) is misbehaving, sending too little water through the heat exchanger so it is getting overheated; the system THINKS more water is actually flowing through that pathway and is over-correcting by tempering with too much cold water.

He took lots of pictures, some video, images of all the diagrams for this unit, and will get on a chat with Rinnai; he knows the script the techs will walk him through and has all the answers ready to go; they might have additional suggestions but he's sure it's valves. Parts are within warranty so I'm just on hook for labor. There's also a bunch of crust on a fitting above the pressure relief valve; he'll get a replacement for that (it's on backorder, apparently) while still under warranty so that I have the part on hand if replacement is ever required.

He also told me to make sure when I descale the system to have the system running hot then pull the plug so the valves stay in the open position; he said following the instructions of "turning off" the system is likely to have it in a configuration where not much of the descaler goes through the exchanger. He gave me Whitlam Flow-Aide Flow32 (a quart, to be added to a gallon of water). I ran a descale process as he directed and definitely got a bunch more crap out than usual. I left it running for two hours while I took some calls; the heat from the flush pump warmed the 1.25 gallons of solution quite a bit. Not sure if it was the valve positions, the different solution, the warmer temperature due to time, or simply amount of time flushing, but there was a bunch of visible grains of crap in the bucket afterwards. I flushed the system very thoroughly with tap water afterwards. At this point it should be clean as a whistle. No impact on the problem though (I didn't expect any impact).

I should hear from him next week with an estimate for when he will have the replacement parts. I will give a further update once there is something to report.

 

[Twowaxhack]

If the outlet temp is out of spec the unit should throw a code. That’s a very important safety feature that’s not working properly.

My vote is the brain is bad. I’ve replaced more brain boards than flow sensors on Rinnai for sure.

 

[Twowaxhack]

If the unit is over 12 yrs old, I’d just replace it. Not worth the money to repair it unless it’s a simple repair. They age out of parts at around 16-18 yrs old anyway.

 

[ColdWaterSandwich]

If the outlet temp is out of spec the unit should throw a code. That’s a very important safety feature that’s not working properly.

My vote is the brain is bad. I’ve replaced more brain boards than flow sensors on Rinnai for sure.

If the unit is over 12 yrs old, I’d just replace it. Not worth the money to repair it unless it’s a simple repair. They age out of parts at around 16-18 yrs old anyway.

The unit just turned 4 years old in October. Parts are under warranty, so I'm on hook for labor only. No where near replacement.

I asked the tech about the surprisingly high HEX output temp, once he pointed out he usually sees that temperature much closer to the set temperature. He didn't believe it was out of spec even though it was unusual, though he said I was likely close to tripping it; he can force high temp errors electronically. So, doesn't seem that the brain is bad, but he was going to give all this info to Rinnai. Who knows, they may throw a board at it. Fine by me.

He reminded me that I'm at a pretty high temp rise over incoming water temp (48-50F incoming, versus 125 as my usual set point) so the system is probably by design getting the water pretty warm so that tempering it doesn't result in overly cold output... if the system were working properly. He's convinced the valves are not responding in a snappy manner, or there's a flow obstruction somewhere, so less water than expected is going through the HEX, leading to exactly the symptoms we are seeing.

Once he's got the diagnosis and parts on order I'll update!

 

[Twowaxhack]

The unit should throw a code if it’s doing what you’ve described in this thread.

The temp shouldn’t not drop, the flow is choked until the unit can maintain temp. It’s not choking the flow to maintain temp and it’s not throwing an error code on the outlet temp dropping below set point.

 

[ColdWaterSandwich]

That's why I wish things like this maintained diagnostic logs that are timestamped with parameters... It would eliminate a lot of guesswork.

 

[Twowaxhack]

That's why I wish things like this maintained diagnostic logs that are timestamped with parameters... It would eliminate a lot of guesswork.

It should never do what you’re describing and not throw a trouble code. That’s why I think the brain is bad.

You should be getting a code 32. Outlet temp fault. It’s not maintaining the outlet temp is what you’ve described and you’ve checked for a crossover.