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oily film

Bill H.
Bill H. Member Posts: 30
My hydronic heating system copper piping inside surfaces are coated with a thin oily-like film, black in color. My Laars boiler has copper coil and the only cast iron is a short tee to which is attached a low water cutoff sensor. Any idea what this film is caused by, if it is necessary to remove, and, if so, what chemical to use.
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