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Corrosion on tankless heater

zepfan
zepfan Member Posts: 359
The attached picture is of the corrosion on an oil boiler’s tankless heater. The heater is only 18 months old, and about six months ago the mixing valve’s screen (not shown) plugged up with sediment, and flow stopped. The house is on well water, and the owner has said he has had a water treatment company out, and they have said the water is fine. The only thing that I think would be causing this condition of the water. Any thoughts, or ideas would be much appreciated. Take care all.

Comments

  • zepfan
    zepfan Member Posts: 359
    I forgot to add in my original post that the elbows attached directly to the heater are stainless steel
  • mattmia2
    mattmia2 Member Posts: 7,171
    Is it leaking on the dhw side or where the taping is welded to the plate on the boiler side? Looks like either threads that didn't seal right or a factory defect in the tankless.
    109A_5zepfan
  • zepfan
    zepfan Member Posts: 359
    Thanks for the response. Even when the system has been off for several hours, there is no signs of water. A leak is what I first suspected.
  • Jamie Hall
    Jamie Hall Member Posts: 20,455
    The condition of the water might or might not be relevant -- but the water has to get to that location first. That means a leak. It is more likely that it will drip when the system is running hard than when it's been off -- indeed, that may be the only time it leaks. I'd agree with @mattmia2 as to where the leak might be -- and my first guess would be the threads.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    zepfan
  • BDR529
    BDR529 Member Posts: 260
    Overly softened water can cause problems. Remove tankless and plate it. Nice indirect with a Fat Anode (Heat Flow, Stainless w/Anode) Replace the anode once a year till you can get an idea of rate of dissolve!

    You got a well,possibly ovely softened and it's a tankless
    zepfan
  • MikeAmann
    MikeAmann Member Posts: 682
    Did you use teflon tape AND sealant at those threaded connections?
    zepfan
  • pedmec
    pedmec Member Posts: 713
    i noticed you said that you used a stainless steel 90. you might be suffering from electrolysis. what did you use for a nipple into the female adapter on the plate?
    zepfan
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,127
    A small leak and because the tankless is hot all the time it boils off and makes corrosion the leak is not seen
    zepfan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,954
    If it is bothering you, then you should disassemble the subject fitting clean it with a wire brush, put a coat of fresh paint on the coil face plate and put a brass nipple with a good thread sealant into that coil tapping. Some will tell you to use teflon tape and pipe joint compound. This is what I have done in the past. the problem is getting it tight enough and also pointing it in the proper direction. Never turn that fitting backwards to get the elbow to line up

    Since you have a new boiler (18 months) you may want to take a 1/4 turn on all the coil plate bolts. You won't believe how loose they are, since that gasket has been heated and cooled several hundred times. This will keep that gasket from leaking and looking like that fitting does.
    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
    zepfanMikeAmann
  • zepfan
    zepfan Member Posts: 359
    Thanks to all that responded. While the tankless heater is 18 months old the boiler is 20 years old. the nipples that go into the heater are stainless and were wrapped with one turn of teflon tape, then pipe dope over top of it. The 90's are stainless steel, and then a copper male is screwed into them. Originally brass were ordered by the supply house that supplied the heater said they were no longer carrying brass and were only carrying stainless. Thanks again to all
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,954
    edited August 2022
    zepfan said:

    Thanks to all that responded. While the tankless heater is 18 months old the boiler is 20 years old. the nipples that go into the heater are stainless and were wrapped with one turn of teflon tape, then pipe dope over top of it. The 90's are stainless steel, and then a copper male is screwed into them. Originally brass were ordered by the supply house that supplied the heater said they were no longer carrying brass and were only carrying stainless. Thanks again to all

    New Boiler or just new coil and gasket. The same thing applies. Give those bolts a 1/4 turn. That new gasket is now 18 months old and will shrink the same way. It don't know the age of the boiler. it just knows its own age. (see that... I said the gasket, an inanimate object , knows its age) That is an example of personification in case @Alan (California Radiant) Forbes is watching.

    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
  • MikeAmann
    MikeAmann Member Posts: 682
    One wrap of teflon tape is not enough. 3 wraps minimum - more as the fittings get larger.
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 7,171
    MikeAmann said:

    One wrap of teflon tape is not enough. 3 wraps minimum - more as the fittings get larger.

    especially if the threads on the stainless were a little out of spec.

    I'd put some anti-seize or teflon dope on those studs although the brass nuts should keep it from seizing in itself.
  • zepfan
    zepfan Member Posts: 359
    I went by the job today and removed the aqua stat to get a better look . It appears that the head of the tankless heater is where the leaks are developing. The surface is wet and appears flaky. A picture is attached