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Mysteriously Drained Boiler

Lorh Member Posts: 2
Hi, I'm a new homeowner and new to steam heat maintenance. To my surprise, I found a nearly empty furnace, a full bucket under my blow down pipe, and water about .5 inch above the bottom of the gauge glass. I've been clearing sediment every week and just looked at it on Friday. I'm concerned about my low water cut off; the self-feeding pump usually kicks in much earlier than it did.

Any thoughts on what could cause this mysterious draining? I tightened a nut on the handle and there doesn't now seem to be a leak. Is there a visual inspection I can do on my own?

My furnace is a Weil mcClain eg45



  • Rod
    Rod Posts: 2,067
    Boiler Water Level

    Hi- Welcome to the “Wall”!   Attached is the I&O manual for your boiler. If you look at Fig. 18 on page 14 you will see that the boiler’s designed waterline level is 23 13/16 inches measured vertically from the base. This is what the waterline should be when the boiler isn’t operating and cold.   Use a Magic Marker and mark this height on your glass sight tube.  With the boiler not operating and cold, use the manual fill button on your water feeder to fill the boiler to the mark on the sight glass.  I might mention that when ever you add fresh water to the boiler turn on the boiler and bring the water to a boil as this drives off excess oxygen in the water which can be very corrosive and shorten the life of your boiler. Once you have established the correct waterline then you can monitor the water level regularly and determine if you have a leak in the system. The leak could be either a water leak or a steam leak.  It sounds as though your blow off valve on the LWCO (Low Water Cut Off) is the source of your leak.  The LWCO should be taken apart and cleaned annually and replaced every ten years. 

    As to the waterfeeder, what make/model do you have? As there can be problems with automatic water feeders, a lot of the homeowners on here use the manual fill instead.

    There are some very good books in the Shop section of this website. I would highly recommend you get one called, “We Got Steam Heat!” as it will be a great help to you.        


    It’s easy reading and written for the homeowner new to steam heating. An evening or two of reading will put your knowledge of steam heating light years ahead.

    You might also want to look in the Resources and Systems section at the top of the website page as there is a lot of good information on steam systems there.

    As the heating season has just about ended, you have plenty of time to read the book and decide what maintenance you need and areas you should leave to pro.  If you have questions don’t hesitate to ask them.

    - Rod

  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,846
    Need clarification.

    Do you have an automatic water feeder on your boiler?

    If so, does it have a bypass valve?

    Have you been relying on the feeder to maintain the water level instead of refilling it manually?
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • Lorh
    Lorh Member Posts: 2
    edited April 2013
    No leaking now

    Thanks guys, I have an automatic water feeder but I manually fill to keep the water line half to 3/4 full in the gauge glass. I'll check the manual Rod posted to be more accurate. The automatic would kick in while I blow down to flush the sediment but it would before reaching the safe minimum water level.

    The plate on the water valve says McDonnell no 101.

    No leaking since my last post but it really hasn't been cool enough to run the furnace lately.
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