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brown sludge vs black sludge

I bought the house last winter in the middle of the heating system. So this is my first time starting the system after the summer. So opened the mud leg valve, boiler valves, LWC, etc., to bleed and remove the crud from the bottom, and refilled the water level, before firing it up for the first time tonight.

Before firing it up the crud was that familiar brown rusty look. But after the boiler was on for a short while, it all turned black. The water level glass was almost pure black, and the water out of the low water cut-off was also black. Is my boiler trying to tell me something?


  • moneypitfeedermoneypitfeeder Member Posts: 231
    just a homeowner,

    But the reddish sludge is rust, and as for the black, well I've found areas in my return piping that I've been opening and cleaning out that are completely clogged with "stuff" and when I'm cleaning that stuff out, and rinsing it it's running black. My only guess on that is carbon, and soot? Maybe even some from when there was a coal boiler installed? My suggestion is to get someone in to flush the returns and clean/skim the boiler. Good Luck!
    steam newbie
  • Jean-David BeyerJean-David Beyer Member Posts: 2,530
    How could that be?

    I do not see how anything from combustion (e.g., coal dust, soot, etc.) could get into the water of a water or steam boiler unless there was a very serious leak in the heat exchanger. Even if the heat exchanger had a leak, to get stuff from the fire side to the water side would require more pressure in the combustion chamber than on the water side. For a hot water system, that would imply pressure in the combustion chamber in excess of 15 psi, and I cannot imagine that. For a low pressure (but not vacuum) steam system, you might need 8 ounces or more pressure in the combustion chamber. I do not know the facts, but intuitively, that sounds high too.
  • Joe VJoe V Member Posts: 233
    edited October 2011
    It is likely

    to be microbes growing in stagnant water with rust and even, possibly, oil.  That is why it has a strong smell.  Drain, fill, boil, cool, drain, fill, boil, cool, and drain again.   Any impurities will work against your ability to steam efficiently.
  • TomMTomM Posts: 233
    iron oxides

    There are many forms of iron oxide.

    The black form is magnetite, Fe3O4.

    The red form is hematite, Fe2O3.

    Not sure if that tells you anything about the chemical makeup of your system.
    beautiful Conshohocken PA
  • Joe VJoe V Member Posts: 233
    Black sludge

    That sulfer smelling black water is from Microbial Influenced Corrosion.

    About the only practical thing you can do to slow it down is to fill and drain as stated earlier and boil during heating season.  But, during warmer weather, summers, it will be back.  I say live with it and try to manage.  Chemical treatment is an expensive alternative.
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