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Steam boiler loses water when off.

Dima Member Posts: 3

I have a one pipe steam system with Weil Mclain boiler.  About 3-4 weeks ago I filled the boiler with fresh water to 3/4 of the glass tube. Today I noticed that water level dropped to 1/4 of the tube and the low water cut off light is on.

There must be a leak somewhere, but I am not sure where to start looking. I did a quick check of the return lines, but do not see any obvious signs of leaking. Any suggestions as to how to find it? Could it be inside the boiler?

Thank you in advance.


    STEAM DOCTOR Member Posts: 1,652
    Buried returns

    Do you have any underground returns? If yes, then they are a likely culprit.
  • Jamie Hall
    Jamie Hall Member Posts: 21,094
    Buried returns

    are surely one place to look.  Could also be a leak between sections or even a rusted out place so yes, inside the boiler is a possibility!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Dima
    Dima Member Posts: 3
    inside the boiler


    Thank you for your responses.

    I don't think the returns are the problem, as the water level stays constant once it drops to a little less than 1/4 of the glass tube.

    I am inclined to think there is a leak inside the boiler somewhere. I did check underneath the boiler (where the burners are), but did not notice any water or wet spots. Maybe because it takes 4-5 weeks for the water level to drop, the leaking is very insignificant and hard to notice?

    How dangerous is it to have this kind of leaking on the inside of the boiler?


    Thank you.


  • Jamie Hall
    Jamie Hall Member Posts: 21,094

    no, probably not -- so long as your low water cutoff is working properly.  If, for some reason, it wasn't and you had only one (a lot or residential boilers do have only one) then there is the possibility that you could unknowingly dry fire the boiler -- and that is very dangerous.

    So is adding water to a really hot boiler (not normal small additions, but coming down, finding the boiler off, and adding a lot of cold is not recommended...).

    On the other hand, I've yet to know of a leak which  got better with time, so it would be well to find the leak and fix it.  Which may mean, sadly, a new boiler.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 15,987
    If it drops down to a certain point and stops

    look to see where the Hartford Loop connects to the boiler piping. If that point is where the water in the glass stops dropping, then the leak is in the return lines.  
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Abracadabra
    Abracadabra Member Posts: 1,948
    edited September 2014
    Another idea..

    Try filling the boiler so that water reaches the header. A bit more height of water might give you a bit more pressure and more leaking water to track down the leak. You can guesstimate if the water has reached the header by feeling if the header is cooler as the cold water enters the header. But yeah, a buried return and/or a leaking section. There's really no where else. This might be a bit obvious for some, but I don't know your level of expertise. I assume there's no leaks at any fittings/nipples attached to the boiler right? Like behind/at the jacket?
    STEAM DOCTOR Member Posts: 1,652

    You can also calculate water height by attaching hose to boiler drain. Raise outlet side of hose to height of header. When water starts coming out then you know that the water has reached the header
  • Water level

    Good idea, and if you use a longer transparent hose,hung up high on the ceiling, you can see how high the water level rises in the wet returns at the pressure which is set on the pressuretrol.

    This will demonstrate the importance of keeping the pressure low.--NBC