Problem with Rinnai 94LSe

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80grit

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First off, I am new to the site. Hello everyone, and thanks for your contributions.


I have a Rinnai 94LSe outdoor propane water heater. It's right at 5 years old, and we started experiencing problems with reduced flow in our bath tubs about a year ago. The reduced flow has been consistent, but there have also been spells of inconsistent temps and even hardly any flow at all. Those spells were infrequent, and we tolerated it. They have become more frequent, and the burner even shuts off if I try to increase demand for more hot by using multiple fixtures at once. I have done everything I know to do. Here is what I know:

-The heater is rated at 9.8gpm. The cold at our whirlpool tub is over 6gpm. The hot starts at the same flow, but shows down to less than 3gpm when it finally comes up to temp. It takes 15-20 minutes to run a bath.

-I'm not getting any error codes at all.

-I have a consistent pressure of 85psi throughout the house, including each side of the heater.

-I flushed the tank with white vinegar for an hour. There was a lot of dark material in it, so i did it again the next day. No real noticeable improvement. I have checked the filter several times since, and it's all clear.

-The burner has a nice, even blue flame.

-The vent is all clear.

- I have been using the pressure release to valve to watch the burner as I increase flow. If I just open it to full flow and once, the burner kicks on, reduces flame height, and then settles in for about 15-20 seconds before it just shuts of. If I open to about half flow, it will stay on but not get very hot. If I start slow and steadily increase flow, it gets really hot until the flow is too much and it shuts off.


Any ideas. I have held out calling the installer because I am stubborn, but I've exhausted my options.
 

Dana

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It's pretty common for tankless hot water heaters to develop lime deposits in the water side of the heat exchangers over time. The harder the water, the more rapid the accumulation is and if you waited until it was narrowed to where you can't fill a tub in a reasonable amount of time the deposits could be substantial. The standard method for de-liming a tankless is to get a few gallons of food-grade white vinegar and a small circulation pump, and pump vinegar through the tankless (power & fuel off) for an hour or so, which you have done. Sometimes it takes somewhat stronger acids than that, but consult manufacturer before using anything stronger than white vinegar. The fact that it's coming out with dark gunk means you have SOMETHING built up in there, it's a matter of figuring out what, how much, and the right treatment to clear it out.

Some folks swear by CLR or Lime-Away as a quicker relatively safe way to go. Those types of products are mild enough that it won't void the warranty with Noritz, but I'm not sure if that's the case with Rinnai. Others use a 50/50 dilution of muriatic acid / water or phosphoric acid (hard core rust remover) solutions to deal with really stubborn deposits, which probably would void the warranty. If you can clear it up with the more aggressive stuff and do annual maintenance flushes with vinegar the amount of potential damage is bounded.
 

80grit

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I haven't noticed any scale buildup, and I don't think it's an issue in my area.

I was really confused after the first flushing. There was chunks of stuff much larger than the pre-filter screen. I can't imagine how it even got in there. There were even perfect 1/2" circles of what appeared to be leaves, but I couldn't make it out for sure. Other than the debris solids, the vinegar was still very clear. When I initially tried to run the water in the tub after, debris nearly completely stopped the flow at the faucet. I thought surely that was the problem, but didn't notice any significant improvement. after i got everything cleaned out.

I did another flushing the following day. It flushed out a few more bits, but nothing significant. I haven't noticed any debris at the faucets since.


I know these things have a minimum flow or they shut off, but why would it shut off for a higher flow? ...and not give an error? It shows the ability to at least pass a high volume of water, so it makes me think it's less likely to have an obstruction. It's like there there's some lazy component in there that says, "This is all I want to do. Anything more, and I'll quit."
 

Dana

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If you have large chunks of organic matter clogging things up in there you need a better filter than the crummy screen. Vinegar MIGHT soften it up enough, but you may need to run a flush using an alkaline rinse (say, a dilute sodium hydroxide drain cleaner solution). Don't do that right after an acid treatment though- the reaction can be too violent.

If the flow detector is being hampered by crud it could be mis-sensing the flow even if it gets a enough of an initial surge at the beginning to light-off. The manuals have instructions on how to measure it's resistance, but you may have to pull it completely out to see if it has foreign mateirals gumming up the works. If it's sensing zero flow for some mechanical reason it won't spit a code, it'll just turn off.
 

Jadnashua

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The calcium buildup, once dissolved in the acid, does not necessarily change the color of the liquid. If it loosened small chunks that have not yet dissolved, you could see those. If the deposit is very thick, it can take quite awhile to dissolve away. If there are some other minerals in there than calcium, it could have other colors, but again, for the most part, once dissolved, they are clear once in solution but not as still solids.

For a tankless to work, it heats the water fairly aggressively, and it will precipitate out more minerals than a typical tank type heater. Unless you have soft water, you really should delime it annually.

Throw in that the seasons are now producing colder ground water, and the tankless has a harder job to do.

I do not know what type of flow sensor is used in that system, but mineral deposits could prevent it from working properly, keeping the thing off, or having trouble regulating the burner to get consistent temperature outputs.
 

Dana

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The flow sensors on tankless heater are usually on the cold-water plumbing side, ahead of the heat exchanger, and not prone to liming up. The lime deposits are almost exclusively in the heat exchanger. From the description sounds like there was some sort of major crud coming in, either chronically or in one slug (perhaps after a water main repair?) that may have jammed something up in the flow sensor, and possibly limited flow to the heat exchanger - hard to say without dissecting it a bit. But dark chunky cruddy bits is NOT a descriptor of lime deposits. Maybe the chunks of stuff was part of the flow detector or some gasket material, since they were bigger than the grid aperture on the filter screen?

m_zU4wqykcVwEddUQzCuAzQ.jpg


The Rinnai flow detector in the above picture has some dark O-rings and dark plastic pieces in contact with the water flow.
 

80grit

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All the crud seemed organic - leaves, bark, and some prices even looked like pine cone pieces. It was hard to tell, but that's the best way to describe it. I definitely didn't feel like it was pieces of heater part. But, how would organic prices get in there in the first place?

Is it possible for a mineral buildup to turn black?
 

80grit

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I ran some diluted CLR through it for 30 minutes today. Nothing came out that I could see, and I didn't see any difference in performance.
 

Dana

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If the flow through the unit seems pretty good I'm guessing it's a flow sensor problem that the internal controls are unable to self-sense. Pull it out for test & inspection.
 

80grit

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Plumber came out yesterday and said everything looked okay. He tested the gas flow and said it drops off to nothing under heavy load. The gas company came out and swapped out the regulator, and everything works great now. Go figure.
 

Dana

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Poor gas pressure would cause most tankless units to spit an error code and stop, not just flame out. That's a rare sort of thing to happen after running fine for years too.

But you probably have the cleanest tankless heat exchanger in the state by now! :)
 
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