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Boiler sight glass - Possibly clogged?

Hi all,

Relatively green when it comes to steam boilers. I have been on here lurking for a while so I know enough to be dangerous but not enough to be useful.

I had my boiler serviced as part of my annual contract with my oil company. After I noticed the sight glass was completely full of water. I let the heat run for a while to see if the level moved, after a long time - it did not. I did a blow off to see if that would adjust the water - nothing. So I turned it off, let it cool and removed the glass. In the process...I broke the glass but also learned how to replace it. I played around with the valves when it was off and the lower valve produced no water even when fully open. I added some water to the system to see if it was low - but nothing. I sort of fished around the valve with a pipe cleaner but I was hesitant because I didn't want to damage anything and have no idea what I am doing. So my question to the group - is it possible its clogged? If so, likely with what? Just sludge? Can I prod it some more with a thicker gauge wire maybe? Should I try to drain the entire thing and take off the whole valve (that seems like a lot). Could it be something else? The gauge does fill with water, but it seems to be from condensed steam from the upper valve.


  • Abracadabra
    Abracadabra Member Posts: 1,948
    Sounds like the bottom valve is clogged. Either remove it and clean it, or replace it.
  • Fred
    Fred Member Posts: 8,518
    Why not call the service company back? Is the top valve on the sight glass fully opened too? It should be. If it is it sounds like the bottom valve/boiler tapping might be clogged. Let the boiler cool down, take the glass out again, put a bucket under the valve and open the bottom sight glass valve. Stick a wire into it and open any clog (the inlet may be pluged). You are not going to hurt anything as it just goes into the boiler block). When water starts to flow, close the bottom valve and replace the glass. Make sure both top and bottom valves are open.
  • Abracadabra
    Abracadabra Member Posts: 1,948
    the gauge glass fittings do a 90, so getting a wire into it to clean it adequately might be difficult without removing it from the block and getting into it from both ends.
  • unclejohn
    unclejohn Member Posts: 1,757
    I just took top and bottom gauge glass valves out and cleaned them with running water. Easy peasy japanezzy.
  • JeffM
    JeffM Member Posts: 178
    Some gauge valves have a little ball check in them to minimize the leak from a broken gauge glass. Normally the ball is out of the way and allows the minimal flow that keeps the level in the glass, but without the glass if the valve is open the ball gets pushed into the flow path and water pressure holds it there.
  • Big Ed_4
    Big Ed_4 Member Posts: 1,896
    Loses the packing nut and turn out the valve stem then cut an metal coat hanger to clear the passage, let it run out clean..If clean your boiler is overfilled.. If so why ... Should be 1/3rd high
    I have enough experience to know , that I dont know it all