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McDonnell-Miller 101 leaked, over-filled boiler

Over the past weekend and Monday I prepped the steam boiler and radiators for the coming heating season, and I lit the boiler pilot on Tuesday, and fired it long enough with only two radiators on to trigger the Vaporstat at 12oz. The thermostat is still set to off, but we have thought about using it soon.

Today I went into the basement and noticed that there was some leakage around the sight glass, and then realized that the sight glass was completely full of water. That was _not_ the case when I finished on Tuesday. I did not think to check the reading on the pressure gauges before I shut off the supply valve to the filler and began draining the boiler down to roughly mid-point on the sight glass. From the sound and the time it took to drain out, I think the near piping was full, but no water was dripping out of the main valve (Barnes & Jones Big Mouth). Assuming that I can fix the filler by replacing the cartridge and filter, (and failing that, replacing the filler), what else do I need to be concerned about? The leak in the filler is apparently fairly slow, since I cannot hear water running, but leaky enough.

The two pressure gauges (5 & 15 lb) and the Vaporstat are on a loop which I fill with distilled water when I replace it after annual cleaning. Above the loop there is a union and then a three-way split, with the gauges and the Vaporstat each on their own short vertical.

The red arrow shows where there was a drip of water, so water got at least as high as that. I have re-done the joints on both ends of that short iron pipe.

Thanks for your attention.


  • Steamhead
    Steamhead Member Posts: 16,901
    I'd completely replace that feeder with a Hydrolevel VXT, which will keep track of how much water has been fed into the system.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    EBEBRATT-Ed Member Posts: 15,629

    Rebuild or replace the feeder everything else will be fine...........no harm done, any water in the system will drain back to the boiler...the beauty of steam and the controls will be fine.

    Before you buy an expensive feeder do you have a manual bypass fill valve that could be leaking by??
    Ken Johnson
  • Ken Johnson
    Ken Johnson Member Posts: 27

    Thanks for the encouragement. No, no manual bypass. After replacing the cartridge and filter, the water level has held steady for more than 12 hours. I will check again at 24, but right now it looks good.