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Too much water in the sightglass

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One pipe steam system noisy, banging, I think it is overfilled. There is a Sterling Condensation pump, a low water cut off and a 57FT Float and Thermostatic trap. When I blow off the LWCO the boiler will fill and stop at the correct height in the sight glass, but over a few days the system overfills and sight glass is full. I opened the lowest wet return and there was not much to flush out of there. Also replaced the float assembly in the 57FT. The Sterling is a single pump. I cannot read the nameplate, but it looks like a 4200 Series from the documents I have read online. Is the pump controlled by both the LWCO and the float switch?

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  • Jamie Hall
    Jamie Hall Member Posts: 23,426
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    Where does your fresh water feed come in? And is there a domestic hot water coil?

    If the fresh water feed comes into the condensate tank, and the valve is leaking slightly, and the condensate pump is controlled by a float in the condensate tank, if the fresh water feed valve is leaking it will overfill -- guaranteed. Even if the fresh water feed goes direct to the boiler, that combination can overfill.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • paul_81
    paul_81 Member Posts: 27
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    I think the Fresh water goes to the condensate tank. I will check tmrw. The float would control both the fresh water valve and the pump to put water back in the boiler? How does the system typically "know" when it is putting condensate back into the boiler rather than fresh water?
  • Jamie Hall
    Jamie Hall Member Posts: 23,426
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    It doesn't. The trouble with condensate tanks is that they have no clue as to how much water the boiler needs. Float too high? Off they go. I do not like condensate tanks. I don't mind boiler feed tanks -- which are controlled by the water level in the boiler -- provided they are really needed. But condensate tanks, controlled by a float in the tank, are nothing but trouble.

    The most likely way your fresh water feed is being controlled is by the LWCO -- most of them have an arrangement where they will feed at a slightly higher level than they will cut off the boiler. So... if you slightly slow condensate return (not unusual) your auto feed calls for more water -- to the boiler. And feeds it. Then the condensate returns to the tank, the tank float says water is to high, and the condensate pump runs the water to the boiler. Which is now overfilled...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England