Does Hard Water Cause the Heat Exchanger to Leak?

Discussion in 'Tankless Water Heater Forum' started by WorldPeace, Jan 30, 2021.

  1. WorldPeace

    WorldPeace New Member

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    I know that hard water can lead to inefficiency due to the lime accumulating on the heating rods and it can cause leaks on an air purge valve. However, can it cause heat exchangers to leak? Tech support at Navien claimed this but when I asked how, he couldn't come up with an answer. I've looked online and I can't find anything about this.

    Does anyone know of any chemical reaction that would cause the heat exchanger to leak due to water hardness?
     
  2. fitter30

    fitter30 Well-Known Member

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    It's not a chemical reaction. Lime is a insulator with condensing boilers holding such little water and their tubing in the heat exchanger is inhanced only a few thousands can cause a failure. Firing rate is adjusted by temperature of water out so with burner running at a higher firing rate causing hot spots and premature failure.
     
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  4. WorldPeace

    WorldPeace New Member

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    Fitter, how would that cause a heat exchanger to leak? For example, heat exchangers might leak due to acid caused by soot and condensate. How would the lime lead to leaks? I've worked with steam boilers for 20 years and I've never heard of lime causing leaks. Fresh oxygen, yes. But, lime? How?
     
  5. fitter30

    fitter30 Well-Known Member

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    Heat exchanger is 100% aluminum the heat exchanger is made so efficient that it can't take being over heated . Hot stops can weaken the tubing, heat exchanger worst case to melt. Haven't seen condensing boilers fail but copper fin tube seen thoughts fail bursting tubes like they were frozen and twisted up like a pretzel
     
  6. WorldPeace

    WorldPeace New Member

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    Fitter,

    Can you cite a source for your claims. I can't find anything online about what you describe. I'm not saying you're wrong but I would like to understand the actual chemical or physical mechanism.

    From what I've read, hard water would actually prevent corrosion while soft water promotes corrosion.

    Also, assuming the tubes fail, how would it cause the inner lining to leak? The heat exchanger casing is not made up of aluminum.

    Thanks for your helpful info or links.
     
  7. fitter30

    fitter30 Well-Known Member

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  8. WorldPeace

    WorldPeace New Member

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    Just wanted to let you know that I already did online research prior to posting here. In none of the links you provided does it state how lime buildup results in a leaking heat exchanger.

    To be honest, I really can't think of a chemical or physical reaction that would lead to lime contributing to a leaking heat exchanger. I've been maintaining two commercial steam boilers for 20 years. And, I've never seen lime buildup as a reason for a leaking boiler. Constant fresh water, yes. Standing water, yes. Soot, yes. Condensate, yes. But, lime? I've seen lime and rust cause 1'' pipes to narrow to pinholes over 100 years and traps to malfunction but I've never seen it as a cause of leaks.

    I admit that this isn't the same as a residential tankless water heater so that is why I am asking here. However, I'm thinking the principles should remain the same since it's the same heating system at work. The burner is heating up the coils. If there is scale buildup, it occurs on the inside of the coils. How would it lead to the deteriation of tank which is located outside of the coils?
     
  9. fitter30

    fitter30 Well-Known Member

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  10. WorldPeace

    WorldPeace New Member

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    Hi, Fitter,

    I appreciate your effort but the link doesn't state anything about how lime would cause a heat exchanger to leak. All it states in general:

    "The hotspots created by limescale can eventually lead to cracks on a heat exchanger.

    This can cause the exchanger to leak. If this is the case, you’ll notice the boiler leaking from the bottom of the casing."

    This doesn't explain anything at all. We all need to be very careful of spreading misinformation. How it starts is that one person simply states an opinion and writes about it. Then, another writes an article and uses that opinion as a source. Then, another article uses that article. Opinion soon becomes fact. This is why people need to rely on primary sources and cite them. In your link, it's a website that gets paid for referrals. It has no legitimacy.

    I'm still not saying you're wrong but I need to see something that explains the process. I have a feeling that boiler companies are using lime buildup as an excuse to waive warranties. I had one steam boiler whose sections were leaking after 5 years even though I maintained it in excellent condition. The manufacturer states that it was due to the hard water but it was complete nonsense. How would lime cause a steam boiler section to leak only after 5 years? It doesn't make sense. I've had steam boilers go for 30+ years when maintained properly. Further, when I asked, the manufacturer couldn't state a chemical or physical reaction that would cause the leaks.

    If you could point to either specialist who personally witnessed scale leading to heat exchanger leaks or a primary source, I would greatly appreciate it.
     
  11. bgard

    bgard Member

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  12. bgard

    bgard Member

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    hard water is simply water with a lot of different minerals in it, these mineral tend to leach on to the hottest surfaces, which in a boiler is the inside of the heat exchanger tubes, as this mineral builds up it insulates the water from the tubes, now the water can no longer carry the heat out of the tubes,as this happens the tubes (what ever material they are made of) begin to overheat and eventually they will melt or distort out of shape and pull them selves out of the headers and they will leak or pour water out. this can happen in a surprisingly short period of time if the flow rate through the heat exchanger is not correct, increasing the flow rate through the heat exchanger can mitigate the buildup of these deposits by reducing the amount of time the water is in the heat exchanger tubes and lowering the delta T across the heat exchanger, the higher flow can also cause a scouring effect in the tubes and remove the scale as it tries to form. Soft water is the opposite of hard water as it has a lack of minerals in it, which is how a water softener works, it removes the minerals from the water, soft water is not corrosive it is erosive, water will always try to have minerals in it, when very soft water goes through a copper tube heat exchanger it errodes the copper out of the the heat exchanger tubes and any other piping that it goes through, eventually making the walls of the tubes so thin they begin to leak. This is not something that manufactures dream up to avoid covering warranty replacement.
     
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Have you ever tried to boil water in a paper cup? It will likely burn away above the water line, but the heat transfer into the water will keep the paper below it's ignition point. A gas flame can exceed the melting point of aluminum, but that can't happen when water is on the other side as it will absorb the heat faster, limiting the actual metal temperature. If the tubing gets enough thickness of mineral deposits, their heat transfer capability isn't as good as aluminum, and will act like an insulator, allowing the metal to get hotter than the design limits. Some tankless systems have a maximum hardness rating, and all of them require periodic cleaning to get rid of them before they become a problem.

    A tankless heater is one appliance where it is really important to follow the maintenance instructions, not only for good performance, but for longevity, too. If your water is harder than suggested, you might have to shorten the time between demineralization maintenances. Or, if you use more hot water than the norm, as it is a function of the volume of the water used, and how hard it is, so annually, may not be often enough with high volume use and/or harder water than normally suggested as allowed. Have soft water, and you could probably extend those demineralization maintenance routines.
     
    Last edited: Feb 2, 2021
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