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Thread: Weil Mclein steam boiler stays on

  1. #1
    DIY Junior Member
    Join Date
    Mar 2013
    new york

    Default Weil Mclein steam boiler stays on

    Boiler releases water but continues to stay on
    My boiler has run dry a few times,the first /second time the lwco switch shut everything down.Everything went back to normal.It has happened on more occasions and now as I refill it it leaks water for a little while (pressure release ?) and then it stops.Then I'm able to refill it, it runs fine throughout the day, then the next morning I notice water has leaked again and the boiler is running dry again.Is it a problem with the pressure release valve ? How can I check ? Main board ?

    If it's a leak why does it stop leaking for so many hours ?

    Edit:I located two hairline cracks,what should I use as a temp fix ?

    Thank You
    Last edited by Queens; 03-19-2013 at 08:55 AM.

  2. #2
    In the trades Dana's Avatar
    Join Date
    Jan 2009


    Steam boilers in residences would normally be running at under 1lb pressure- if somebody cranked it up, that's a mistake. But it's probably not the root of the problem. It would be surprising to see a steam boilers pressure relief valve spilling water unless there was something really wrong (or grossly maladusted) with the operating pressure control. Steam PRVs on residential systems would normally be 8-15psi, (15psi being more typical) which is several times the ~1psi peak pressure you should see on the system with a correctly adjusted & functioning pressuretrol.

    Hairline cracks in cast iron will leak at different rates depending on the temperature, and differences in temperarture across the boiler would cause it to open up further until the temperatures even-up. When you fill a warm boiler up with cool water the average temp of the boiler drops well below it's operating temp. While filling it the temperature differential is large, which may be why it leaks initially then tapers off when filling. When at full operating temp it may be opening up again. I don't know of a safe & sane temporary repair option here.

    Any DIYer adjusting or repairing their steam heating system needs to own (and read) this book. It'll save you more aggravation & service calls than you might believe.

  3. #3
    In the Trades Tom Sawyer's Avatar
    Join Date
    Nov 2010


    There are several temporary crack sealers on the market for boilers but, they should only be used by professionals and you need someone that knows steam boilers to check your boiler out. Those cracks could be dangerous and you need a new boiler.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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