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cannot find a steam leak

I operate a building with a federal fst 300 one pipe steam system. My boiler is losing about 3 inches of water each cycle. I cannot for the life of me find any leaks in the system. I have had leaks in the past and they become evident in a matter of hours, even in the underground return lines. This present drop in water is going on for weeks now. What am I missing? Any ideas would be welcome.


  • conversiontimeconversiontime Member Posts: 87
    returns are under ground/concrete?

    That is a good bit of water to lose in just one cycle and it makes me think the return condensate is not making it back to the boiler at all. On the next cycle mark the point on the site glass when the boiler shuts down, then see if it rises as condensate returns. You might be able to run a plumber camera down the returns to look for a obvious break. This may also give a good idea of whether the entire line need to be replaced or just a section.
  • JohnNYJohnNY Member Posts: 1,811
    White smoke?

    Have you stepped outside and checked your chimney? Perhaps the boiler has an internal crack and it's steaming out.
    For private consulting services, find John "JohnNY" Cataneo here at :
    "72°F, LLC"
    Or email John at [email protected]
    Or at Gateway Plumbing & Heating
    John travels regularly to out-of-state clients for consulting work.
  • SteamheadSteamhead Member Posts: 11,323
    If the boiler has a feed tank and pump

    to return the water, the check valve between the pump and the boiler may be leaking.

    Is there a water meter on the make-up water line?
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
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    Baltimore, MD (USA) and consulting anywhere.
  • bewilderedbewildered Member Posts: 4
    cannot find steam leak

    The problem is that there are 4 returns that become two returns as they get back to the basement. The funny thing that I`ve noticed is that one of them comes back at about the temp it should, but, the other one never really gets as hot as it should. That leads me to believe that it has a break somewhere. I can see 90% of this return and it looks perfect. I have even put a heat tracer to the portion that is hidden and it seems normal.
  • bewilderedbewildered Member Posts: 4
    cannot find steam leak

    Yep, it looks good.
  • bewilderedbewildered Member Posts: 4
    cannot find steam leak

    It all appears to be ok with the check valve. The return lines are always wet below the boiler water level, so why isn`t it filling up?
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