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Blackened water in system

Tim_41 Member Posts: 153
Also, if the water smells bad thats a good thing. That means there is no O2 in the water.


  • Rob Blair
    Rob Blair Member Posts: 227
    Blackened water in new system

    I received a call from a man who had a system installed in December, mostly in slab radiant. Using a Weil McLain Ultra boiller. He said that after about one month of operation he noticed the pex that he could see, it is some type of clear/opaque variety, was beginning to get black spots, as if there was plac building up inside the tubing. NOw he says it is almost totally dark. Any ideas. BTW, I had nothing to do with this job.

    Thanks, Rob
  • hot_rod
    hot_rod Member Posts: 22,150
    It is fairly common

    to see the fluid take on a dark color. Unless it has a colored glycol, or a hydronic conditioner added it tends to go gray.

    Could be the system was never cleaned and flushed per the manufactures directions?

    If it were me, especially with an aluminum boiler, I would add a Rhomar cleaner, circulate for a few days, flush and refill with a Rhomar 922 conditioner. That would be the best way to protect that investment.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Weezbo
    Weezbo Member Posts: 6,232
    to add a second to the greying of the glycol :)

    nice touch is cherry food colouring on commissioning...looks great for quite a while :)

  • I have "No Freeze" in the last one I did, it's the prettiest shade of blue. ;) It hasn't blackened at all yet. I DID do the TSP wash and rinse plus the only ferrous in the system is the pump casings. It's been running since Oct 06. I understand Wirsbo/Uponor had issues with their flow meters becoming obscured because of this blackening. I believe they now recommend cleaning the system before placing it in service. I can tell you I'm the only guy anyone knows around here that takes the time to clean the system out. It drives my bottom line up over my competitor's but I don't really care. You get what you pay for. My flow meters are perfectly clean.
  • Bob D._2
    Bob D._2 Member Posts: 34
    Blackened Hydronic

    If there is some iron or steel pipe or parts in the system, then blackened water also could indicate the formation of an iron oxide type called magnetite. Magnetite is a tightly adherent, highly protective layer that forms on wetted ferrous (as in cast iron sectionals and steel pipe). When it forms, the iron will no longer (o.k., only very, very slowly) corrode, oxidize, rust, what-have-you. Compare this to the red rust, hematite (like in hemoglobin - the stuff in red blood cells that carries oxygen), which usually means that oxygen is continually getting into your system and corrosion will be accelerated. Black stuff = "good" rust, reddish stuff = "bad" rust. Just one thought from the Peabody's "way-back machine".

  • Yea, I recall someone around here saying black water was like fine wine to a boiler... ;)

  • Yup, dab a little behind the ears before going out. The wethead-ettes can't resist it! ;)
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