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Top of sight glass to bottom in a full cycle?

I’ve got an old Sears/Dunkirk 155k btu boiler heating a single pipe steam system in a ~3200 square foot, 3 story drafty old house. We bought the house last year, previous owners didn’t really take care of it, we got it mostly squared away but understand that it owes us nothing. It’s been surging so I’m going to have my steam guy remove the fitting (looks like it hasn’t been removed in decades) and skim it. 

I noticed that, when going through a full heat cycle (such as during the 16 degree day we had this week) the water level will drop from the top of the sight glass to about an inch from the bottom. With the surging, it even dives below the bottom of the glass and occasionally trips the LWCO for a couple seconds. At the end of the cycle (steam still in the system), the water level will slowly creep back to the top. 

I know some water leaves the boiler, and I’m sure the surging is throwing some water into the header—but I haven’t noticed any wet steam symptoms, but should I be concerned that that much water is “going somewhere”?

Thank you all for this wonderful website and forum! If I missed any details in my question please let me know. 


  • Jamie Hall
    Jamie Hall Member Posts: 23,272
    Well, if it comes back after the end of the cycle at least it's not leaking. That's good. But it really shouldn't all back out lie that -- drop an inch or two maybe, no problem, but back our like that? No.

    Could you perhaps post a few pictures of the boiler and the piping around it, from far enough so we can kind of see how the piping is arranged?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 15,512
    My guess is there is no equalizer or hartford loop