Please help explain confusing steam boiler leak behavior

navinbgs

I have an old Weil McLain EG 45 that powers a one pipe steam heat system for my 1930s built home. Previous owner got copper near boiler piping at some point and the setup doesn’t follow many of the best practices mentioned on this forum. I made minor modifications and despite the piping problems the system has worked reasonably well. So, I left the system alone, thinking I will correct major issues when I finally have to replace the boiler.

Unfortunately that day has arrived. System has been losing water rapidly and needed to be refilled every day. Thanks to the info posted on this forum I tested the boiler by filling water to the top and could see water trickling down in the back of burner box. I am assuming that this means that I have a hole in the boiler above the water line where water loss is happening.

I understand I have to replace the boiler, but curious about the behavior I now see. If I fill the boiler to the regular level, half way of sight glass, and run the system then the water gets used up rapidly. Low water cutoff kicks in in less than 8 hours if system is running normally. However, when I accidentally kept the water lever high, just at very top of sight glass, the water loss seems to be negligible. System is running for hours without water level dropping. 

I tested this a few times. Dropping the water level manually to normal levels and then running the boiler results in rapid water loss in a non observable way (up the chimney?). Don’t see white “smoke” out the chimney, but clearly the water/steam is escaping somewhere. But if I keep the water level very high, but below the apparent leak level, results in dramatically lower loss.

I am working on scheduling the boiler replacement anyway, but would love any insight on why this behavior might be occurring.

Mad Dog_2

I have found The Steam to be very enigmatic and mysterious.  Stubborn, seemingly invisible water losses are worse than hunting down leaks on a natural  gas pressure test.  Is it the boiler block itself?  Is it the near boiler piping? Is it escaping up the chimney? Is it the air vents that seem to work?   Is it a loose threaded joint in a buried wall?  Wet steam leaks are usually very obvious and easy to see and find. It's the Dry Steam leaks that baffle!  No obvious wetness, but the water level keeps dropping.  The only way you can really chase down the leak is isolating everything with valves and pressure testing which is alot of work.  Mad 🐕 Dog

EBEBRATT-Ed

@navinbgs

None the less if you overfilled the boiler and saw water dripping it is most likely the boiler. But it wouldn't hurt to take part of the jacket off and see if you can pinpoint the leak.

Cutting the jacket to get part of it off is probably ok at this point you can run without the jacket in the slim chance you may find a pipe leaking.

mattmia2

The leak is probably between the normal water line and the top of the sight glass so when you flood it some the water covers the leak and steam can flow a lot faster out that hole than liquid water can.

navinbgs

Thank you for your responses.

@mattmia2
Your explanation makes a lot of sense, but I am still surprised at how big the difference in leak rate is. It has been two days in the slightly overfilled state and I see no drop in water level.

Hopefully, system keeps running uneventfully until I can replace boiler.