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Steam boiler suddenly overfilled, Why?

DaveGateway Member Posts: 568
I'm baffled. I woke up this morning and the heat was off. Figuring I need to add some water to the boiler, I go downstairs to find that instead the system is off on high pressure, and the sight glass is completely full.
I had to bleed off 20 gallons in five gallon buckets to get it back down to normal. The system was obviously off for a while because the water and pipes were just slightly warm.

Nobody in the house added water yesterday.

So where does this much water come from?
Could it be possible that one of the rad vents in the system had not been working for a while and the water was trapped by a vacuum? I haven't noticed any of the radiators not heating, but it hasn't been really that cold in Jersey. Maybe the water was held up for weeks, and I've collectively added that much extra water over that time period, then last night the vacuum broke free and flooded the boiler?

My fill valve is a spring cock handle type valve which you have to hold open. Could negative pressure in the system possibly suck water through it? I can hear water as soon as I crack the valve open, and it definitely was not flowing this morning.

Last note. Yesterday morning, sight glass water was a bit rusty, but otherwise the water level was perfect.

Any ideas?


  • bigugh_4
    bigugh_4 Member Posts: 406
    20 gallons in a day or two sounds like a leaky fill valve.

    Self closing valve may have debrie in it. Did you think to feel the supply pipe near the valve, if it is below ambient temp of the room, it is being cooled by the incoming leaking water. Of Course repair or replace the culprit valve.
  • Yes I agree

    with Bigugh , it sounds like a leaky valve . You say it is spring loaded ? Never saw a boiler feed valve like that . Ony saw something like that on the old low water cutoffs . They changed them to ball valves since then , and I would recommend changing that valve to a ball valve also . We install them on a vertical pipe so you have to lift the handle up to add water . No chance of the handle dropping open and overfilling the boiler . At least its a cheap fix and can eliminate one culprit to the problem . Maybe add a union after the valve to make sure theres no leak also .

    The rusty water is from overfilling the boiler . My partner accidentally did that a few months ago and you would not believe the color the water was in the sight glass - and it was a new install . Drain the whole boiler out and refill - try to get all the muck out that came back from the returns .

    We had a problem job last year where the serviceman thought the same thing was happening - on one side of a steam main he thought water was getting trapped in the risers somehow , like holding your finger over a straw with water in it . But I gotta say , 20 gallons sounds like an awful lot to get trapped in a system like that .

    One other thing - there is no automatic feeder on the boiler , is there ?
  • Robert O'Connor_4
    Robert O'Connor_4 Member Posts: 88
    Is there

    a hotwater coil in the boiler?


This discussion has been closed.