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Sight glass full won’t go down

dinosaurposterdinosaurposter Member Posts: 4
edited January 2019 in Gas Heating
My main concern is that my sight glass water level will not go down. It’s been a little touchy in the past with fluctuations but now I can’t get it to go down. I added a little bit of water to the system over a week ago because it was close to the bottom. I did not fill it to the top but now that its filled up it won’t go down. If I take enough out I can start to see it fluctuate at the very top but then it fills back up. I cleaned the glass and the opening below it. Filled right back up. Also, I get loud radiator knocks that I didn’t used to get.


  • neilcneilc Member Posts: 805
    Your showing monster pressure on that gage,
    when did you check and clean the Pigtail last ?
    They are prone to clogging, and also the port where it's screwed into the Low Water Cutoff.

    We don't see your fill valve, do we?
    a picture?
    It may be leaking by, and needs rebuilding or replacement.

    If you shut the boiler off, let it cool, and drain it down, do you see the water level drop down?
    Are those sight gage valves open ?
    And then it's possible those sight gage valves are blocked into the boiler also. They can be disassembled and their ports poked, while the boiler is off and drained down a bit.

    Refill cool, not hot, boiler to mid glass.
  • dinosaurposterdinosaurposter Member Posts: 4
    edited January 2019
    I’ve never touched the pigtail. That high pressure is also new.

    Fill valve is just outside of photo, sorry. It’s the same type of valve as the yellow handled drain valve. I don’t think that’s leaking.

    The two sight valves are open all the way.

    I was thinking about draining it down but it’s cold now and it’s about to go down to zero soon. You think I should try that now or wait until the cold weather moves on?
  • neilcneilc Member Posts: 805
    wait for the weather to pass,

    although I would check the pigtail at least,
    if it doesn't come easy, wait.

    and you can drain down to midglass now also,
    but if it's refilling on its own, ya need to figure out why,
    and it seems it could only be that unseen valve.
    there's no auto filler, correct?
  • dinosaurposterdinosaurposter Member Posts: 4
    Here’s a pic of the valve. Maybe it is leaking. If it is I can’t see or hear it.

    I’ve already taken out 4-5 gallons over the past couple of days.

    Thanks for your help.
  • Jamie HallJamie Hall Member Posts: 12,696
    No domestic hot water coil? Then it can only be that valve -- the water has to come from somewhere. 4 to 5 gallons over the last couple of days may seem like a lot, but... that's about that's about a pint per hour. Or a good size coffee cup every half hour. Not much, when you think of it in those terms.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • FredFred Member Posts: 8,418
    If you have a water feeder, it is leaking and filling the boiler. If you don't have a water feeder, the supply valve is allowing water to pass through it .

    The pressure may be the result of one of two reasons, maybe both:
    - with the water level that high, pressure will rise. Get the water down to no more than 2/3's of the sight glass. It sounds like even when it was working you kept it near the top of the sight glass. That's too high.
    - The other issue is where your Pressuretol is mounted. When they are mounted on top of the Low Water Cut off, that tapping and the Pigtail is 100% clogged and the Pressuretrol can't see the system pressure. I always recommend the Pressuretrol be mounted anywhere other than on top of the MM#67 LWCO or the pigtail and the opening it is mounted on needs to be cleaned at least twice every heating system.
  • FredFred Member Posts: 8,418
    I might also add that while it seems like the water level won't drop in the sight glass, the boiler could be so over filled that you simply haven't drained enough water out for the water level to be in the range of the sight glass. Don't let it overfill until water spills out of you main vents. Turn the boiler power off and drain water until you actually see the level in the sight glass. Then turn the power back on and figure out where the water is coming from.
  • dinosaurposterdinosaurposter Member Posts: 4
    Well I just took out 5 gallons and the sight glass didn’t fill all the way back up. For the record I would never fill the sight glass past half. It was suddenly very high a couple days ago and I didn’t understand why it would keep staying full or filling back up even when I’d drain a lot of water.

    It does seem like water must be passing that valve or a blockage may have messed with the accuracy of my sight.

    The high pressure, knocking, and full glass did both seem to suddenly happen at the same time a couple days ago. Maybe I’m missing something.
  • Jamie HallJamie Hall Member Posts: 12,696
    Don't think you're missing anything -- most likely that's when the valve stared leaking...
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • SeanBeansSeanBeans Member Posts: 482
    Wouldn’t hurt to slap a pressure reducing valve before the feed valve when changing..
    If it doesn’t already have one
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