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Rinnai boiler corroded in less than two years

WigglyWalker Member Posts: 27
Rinnai Q85 wall hung boiler. In less than two years the boiler has corroded around the circulator pump. The aluminum also on the heat exchanger has started to disintegrate. The Rinnai rep is telling me it's because oxygenation, and other people have said it could be electrolysis. Didn't know if anyone else has experienced this or seen this happening to boiler in less than two years.


  • SWEI
    SWEI Member Posts: 7,356
    Have you tested the water?

    pH and chlorides would be my primary concerns.

    The vast majority of boilers are designed to run only in closed systems.  Oxygen ingress will raise pH, but I did not think it would be able to take out those aluminum end pieces.  Another reason we like to shut off the auto feeder once the system has fully purged itself of air.
  • icesailor
    icesailor Member Posts: 7,265
    Fill Valves Off:

    The best part of leaving fill valves off is when the system reaches an equilibrium and the high points can suck in air when the system is cold and contracted. Then, all the air gets expelled when the system expands and expels the O2 poor air. Then, contracts for another cycle of fresh high O2 air. If, when the entire system is hot, you set the system pressure to be at least 25#, and it doesn't drop below 12# to 15", your fine. If it drops below 12#, the expansion tank is too small, regardless what someone tells you.

    Then,it's important to disregard any testing of the water for a low PH which might help electrolysis between the aluminum HX and the copper of the piping. Add some steel pipe and wrought fittings, and you can do a really fine chemistry and physics experiment. On how to dissolve a beer cooler boiler. Especially if you are in New England where low PH potable water is the norm.

    There is also a thing called "Crevice Corrosion that just LOVES low PH water. If you see that white fluffy stuff anywhere, its time to purchase a good quality PH meter and plan on some boiler/system conditioner treatment. Before it gets to that.
  • WigglyWalker
    WigglyWalker Member Posts: 27
    Water tests

    Here are some tests that were done. Still the question of could this happen so quickly?
  • JStar
    JStar Member Posts: 2,752

    One thing that catches my eye is that the drain line is not made with a hard connection. I wonder if the condensate is vaporizing or being sucked into the cabinet by the blower. The acid in the condensate may be causing this corrosion.

    That's just an observation, and I have no proof or experience to back it up.
  • WigglyWalker
    WigglyWalker Member Posts: 27

    Even if it was hard piped, there is an air gap in the boiler case.
  • kcopp
    kcopp Member Posts: 4,189
    I am 99% sure....

    that the Rinnai uses a SS HX...not aluminum. Where is the location of the boiler? Is it in a coastal location? Where in the house? Are there contaminants around? Give us more details plz.... something isn't right here....
  • WigglyWalker
    WigglyWalker Member Posts: 27

    The Rinnai boiler has the older style low loss copper header which is then feeding a 1 inch reverse return radiant loop with Onyx tubing then the other 3 zones of the house has Smith heating edge baseboard with watts radiant oxygen barrier pexs all.

    The boiler in located 8 miles inland and I also installed a Rinnai tankless with zero signs of corrosion.

    I was also told by the Rinnai rep that the boiler is made up of many different metals other than stainless steel.

    Not sure what else you want?

    I installed the same system at my house and I am 1/2 a mile from the ocean.

    The rest if the system still looks brand new. No sign of corrosion on any other fittings.
  • Zman
    Zman Member Posts: 7,447
    Crevice corrosion

    I think Ice is on it.

    The combination of O2 and the low PH makes crevice corrosion seem very likely.

    Combine that with the fact that most of the damage is around welds and gasketed connections with dissimilar metals and I think the cuprit is pretty clear.

    I am guessing this is not the first boiler this house has had. What happened to the previous on?  How was the system purged when this boiler was installed? You likely have a bad "cocktail" that is, in part, made up of the ferrous components of " boiler past"

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • jonny88
    jonny88 Member Posts: 1,139
    agree with bob

    I just did a job .all balancing valves were caked in mud.A lot of ferous materials on boiler but radiant was piped with non oxy barrier pex,ouch.Try reach out to Jack,he is familiar with Rinnai and will troubleshoot you through this I am sure.
  • icesailor
    icesailor Member Posts: 7,265
    Old water, new systems:

    One of the things about well water and Municipal water in New England having a low PH is that you just get used to it. Like old comfortable shoes. 20 years ago the only "Flushing" most us did was to a toilet. If you fill a system and it runs for 20 years, and you change it and don't flush it out, you have 20 years of corrosion by-products in the system and you add fresh water that probably has the same chemistry as the old water. And even if you "Flush" it, if you use the same water, you are just filling it with the same old bad water unless you correct it. In the case of the water samples, PH and conductivity are the danger points. Then, there's all that stray energy running around the pipes in a house. I've seen dialectic unions fail. If you have a house piped in copper, connected to a steel water tank, and all proper bonding/grounding is in place, a piece of PEX or a dialectic union is supposed to stop any current from dis-similar metals. But if the water has high conductivity, can't the current pass through the water and by-pass the block? My sharp electrical friends could never answer that question. But I say that if you have a heating system with lots of dis-similar metals, and a whole tribe of spinning circulators adding static energy into the system which is highly conductive, you have a problem like you are seeing. I saw lots of it. There was no other explanation.

    Then, there's all that energy in the ground from electrical grids trying to balance themselves. Next time you have a spare moment, try this. Take your Digital true RMS Multi-tester and set it to the lowest voltage scale. Pee on the ground, stick one end of the probe in the wet ground and clamp it to a cold water pipe like a outside sill cock. If you get a reading, where is the voltage coming from? Ever been in a house with power/control issues? And you turned off the power and had 14 volts on the neutral> Because the primaries in the street were shot and leaking. They hadn't blown yet. But the bare neutral wires on the primary cable wrap weren't doing the job intended and the power was looking for a place to go. The power company put some sort of a "Trap" on the neutral to stop the back flow. Of course they denied that anything is wrong. And the problem went away when they replaced all the 20+ YO direct buried primary power cable and put it all in conduit.

    Another thing to be aware of is unbalanced 3 phase primary loads where the primaries are trying to balance themselves through the Neutrals/Grounds.  Something that happened regularly where I used to work.

    Why does lightning hit the ground in a lightning storm? Why does your hair stand on end if the strike is going to be near you?
  • Paul Pollets
    Paul Pollets Member Posts: 3,620
    Corrosion Paths

    Another path for corrosion is the combustion fresh air intake. If you're using a uninvent, or the boiler vent is close to the CFA, the boiler can take in contaminated air (Reversion). Had a Munchkin that died in my shop in late Dec. with failed heat exchanger that was pinholed at the top, not the bottom. The appliance was cleaned yearly and the water was treated...
  • SWEI
    SWEI Member Posts: 7,356
    Rinnai boiler HX

    has stainless steel tubes where the flame impinges.  The endplates (where the water loops around) are aluminum alloy castings.  The design has been in use for many years in Europe and has a good reputation.
  • Jack
    Jack Member Posts: 1,046
    Not sure where to go on this...

    Johnny, thanks for the shout-out, but I am waiting to hear the official take on this one. All the previous posts are really helpful, but I can't pin this one down from here. Honestly, I'm not sure I'd pin this one if I was there. I haven't seen one in this condition before.