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Black particles in water: Navien tankless water heater to blame?

cry1130 Member Posts: 1
Small black particles started appearing in our water a few weeks ago. Appears to only be the hot water. We have a Navien tankless water heater. I'm not sure the model but have attached a picture of the inside. Looks relatively new (we bought the house a year and a half ago). We had the Navien flushed/serviced. Did not fix the issue. We had the valve on the main water line into the house replaced as recommended by a plumber (in case rubber is the issue). House has copper and PVC pipes. No visual evidence of flexible/rubber lined piping in the home. We're not sure exactly what the particles are. I have attached a picture. They smear when you rub with your finger. Any ideas as to what this is and how to fix it?


  • Intplm.
    Intplm. Member Posts: 1,603
    Those particle are very hard to see. Are you sure the particles are only coming from the hot water ?

    It could be that the hot water is extracting those black particles out of the water when the water is heated. The thing that I can't tell is how they smear when rubbed.

    A few questions.
    Have you had your water tested?
    Is there a water filter and water conditioner on your water main?
    Is this city water or a well?
    From what water faucet did you take the sample from?
    It could be normal build up coming through your faucets that is built up in the faucet aerators ?

    Maybe remove and clean the aerators on your faucets ?

    Try draping a white cloth like a handkerchief over a glass and turn the faucet on drawing water through the cloth? Then look at the cloth.
    Hope these things help. Please respond back.

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 3,825
    edited February 2019
    Our local water department changed the disinfectant they add to the water from chlorine to chloramine (a chlorine/ammonia compound). The ammonia breaks down rubber, affecting various parts of a plumbing system (toilet flappers, faucet/water heater connectors, etc.); symptoms are like yours. Chloramine resistant fittings are now available.

    What part of the country do you live in? Check with your water department.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,137
    Hello, If you have any braided stainless flex connectors, they often have a black rubber lining that disintegrates just as you have described. An expansion tank could be another source of rubber too. ;)

    Yours, Larry