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Water emptying out while boiler on but refills when off

OHO Member Posts: 1
I have a 1 pipe steam system. The water empties out when it is on and the system occasionally adds water when it is very low (as it should). However, a bunch of water returns when the system turns off and the water goes way above the maximum line (so I empty it out). I tired searching the forum but can't find info. Any input would be greatly appreciated.


  • Fred
    Fred Member Posts: 8,542
    How old is the boiler? Has it or any piping been replaced since it was last skimmed? Many times there are oils on the surface of the water, making it hard for the steam bubbles to break through the surface of the water and that causes water to be pushed out into the wet returns. When the boiler shuts down the water immediately returns to the boiler. Do you have a skim port on your boiler, somewhere above the water line? If so, you need to do a very slow skim to get the oils off of the surface. If you don't, you need to find a tapping in the boiler above the water line and install one so you can skim.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Overpressure can also cause the water level to drop, as the water "hides" in the wet returns. When the boiler is off, the water will quickly return. This when combined with water being carried up into the risers will cause what you are seeing.
    This causes a lot of thermal shock in the sections, and should be corrected as soon as possible.--NBC