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Weil-McLean Drain Question

Hi all. I have a Weil-McLean steam boiler, 4 years old. My plumber told me to drain the water every 2 weeks from the front drain (first pic). Recently it has stopped working. Barely any water comes out. I can still drain from the back drain by the sight glass (second pic). Does anyone know why this front drain may not be releasing water anymore? I open it up fully and it’s just a trickle. Thanks for your help.


  • Jamie Hall
    Jamie Hall Member Posts: 23,289
    Probably plugged up with sludge. They do.

    That said, unless you have a float type low water cutoff there's no need to drain the boiler at all during the heating season. In fact, except for that one item, it's better not to -- fresh water isn't good for boilers.

    What you will need to do, though, is at the end of the heating season you will want to get that drain to flow -- may have to take it apart and clean it all up.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • CiscoJP
    CiscoJP Member Posts: 2
    edited February 2020
    Thanks! I was only doing it because the plumber who installed it said I should flush it about every 2-3 weeks. The one we replaced had a bad sludge problem from the previous owners never flushing it. But the rear one under the sight glass still works. But maybe I’ll get someone in to clean the front drain once heating season is over.
    JUGHNE Member Posts: 11,061
    Those drains are referred to as "boiler drains" but are worthless to actually remove any sludge.
    I would have the tech remove those and add full size ball valves with hose attachment fitting. Best to use brass or SS nipples to install them.
    Then with both hoses connected and open to drain you can add water manually to the boiler to flush out any sludge.
    You don't want to be adding water every week, just do this at the end or beginning of the heating season. Always bring the boiler up to steam to remove any oxygen from the water.

    He could also clean the sight glass ports into the boiler.

    Do you have any other drains on the lower copper line that returns water to the boiler?
    Pictures of the piping along the floor would help, also if you could show all the piping floor to ceiling would get attention from others.