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Pressuretrol doesn't seem to be working - damaged unit or bad installation?

lmoore8lmoore8 Member Posts: 13
edited October 2019 in Strictly Steam
As I'm trying to get my steam system working property in my new house, I started by replacing the radiator vents, which weren't working, as well as replacing the main vents (and significantly increasing the main vent capacity). I also installed new pressure gauges, including a 0-5 psi gauge. I checked the pressuretrol settings, and it was set to about 0.5-1 psi cut in with a +1 differential.

When I tested the system, I watched the pressure rise to over 3.5 psi before I shut it off. So something is wrong with the pressuretrol. I figure either the unit is broken and needs to be replaced or the installation is bad (see picture). The pigtail to the pressuretrol has been cleaned, so I'm pretty confident that's not blocked. But getting pressure at the pressuretrol relies on going though this super old looking low water shutoff, so the path goes below the water line. Does this path make sense? Will the pressuretrol get the correct pressure in that location?

Can I move the pressuretrol anywhere I want that gets steam pressure, like onto the newly installed pressure gauge system (seen partially at the top of the picture) that I know gets pressure? If it still doesn't work properly there, I figure I need to replace it. Does this seem like a reasonable troubleshooting order?


  • Jamie HallJamie Hall Member Posts: 12,718
    What I'd do, anyway. But... while I was at it I'd probably pick up a set of gaskets for that LWCO and take it apart and clean it...
    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
    delta T
  • lmoore8lmoore8 Member Posts: 13
    Is it pretty straightforward to rebuild a low water cutoff? I could also consider replacing it. I have no idea if it even works, which isn't ideal either.
  • JUGHNEJUGHNE Member Posts: 6,796
    Have you ever flushed the LWCO? The sight glass level should drop and the boiler fire shut down.
    IIWM, i would move the ptrol up with the gauges. They all need some form of pigtail.
    Could you post some pictures of the boiler piping, floor to ceiling?
  • FredFred Member Posts: 8,418
    That's a McDonnell Miller #67 Low Water Cut-off. They are still sold, if you want a new one. McDonnell recommends replacement every 10 years but they can be cleaned/rebuilt easily, as long as you get a new set of gaskets, as @Jamie Hall said. Yours is not that old. It has a ball valve on it. The older ones had a spring loaded valve.
    I have the same LWCO and my Pressuretrol was mounted like yours. The pigtail clogs especially quickly when mounted on that port, on the LWCO so moving it is the best thing to do. The Pressuretrol may be out of calibration, Here is the procedure to calibrate it. If, during the calibration, it still doesn't work, a replacement is warranted.
    Calibration procedure:
    Inside the Pressuretrol, right below the micro switch, there is a pivot arm. At the end of that arm you will see a screw pin that is activated by the diaphragm at the bottom of the Pressuretrol. If you look very carefully at that screw pin, you will see it actually has a tiny (I mean tiny) hex head on it. It takes a .050 hex wrench and you can turn it clockwise (Towards the bottom of the Pressuretrol to decrease the Cut-out pressure or counter clockwise to increase the cut-out pressure (which none of us want to do but who knows, your Pressuretrol may be really screwed up!). Turn the power to the unit off first. You may find the first attempt to turn that screw a little bit stubborn (relatively speaking) because it has some Locktite on it but it does turn. Don't turn too much, a fraction of a turn goes a long way towards getting it adjusted where you want it (maybe 1/32 inch turn to start with). You may need to play with it to get it exactly where you want cut out to be.
  • lmoore8lmoore8 Member Posts: 13
    Here are some pictures. I went ahead and moved the pressuretrol up with the gauges. I also tested to make sure the wiring was right by pressing the lever in the pressuretrol manually and it did cut off the boiler. So now I’ll just see if it is sensing and responding to the pressure correctly. Sitting downstairs next to the boiler and waiting is about like watching paint dry though.
  • JUGHNEJUGHNE Member Posts: 6,796
    You need to "blow down" that LWCO at least once a week while the boiler is firing. The fire must shut off as you flush it out.
    A short, maybe 4", nipple screwed into the bottom of the yellow handle valve makes the flushing a little neater and safer as you open it.

    Also, the P-trols may come apart inside if you run the screw down too far, fairly easy to put pack together. Just something to watch for.
  • lmoore8lmoore8 Member Posts: 13
    I just did it, and the flame cut off as I flushed it. I have a bucket that's about the right height to keep the water contained. So it seems like that is working. But I let the pressure build up first, and the pressuretrol didn't shut it off where I wanted. So it sounds like I either need calibrate and/or replace it. We'll see what happens. Thanks for the advice everyone.
  • FredFred Member Posts: 8,418
    @lmoore8 Be aware that even a new Pressuretrol will need to be calibrated, right out of the box. The factory quality control on that process is horrible and they will be off as much as 5 PSI.
  • JUGHNEJUGHNE Member Posts: 6,796
    If the control is installed with a tee on the pigtail that has your 0-5 gauge then in the future you can see what the control is feeling. Also for the future to check the pigtail you just unscrew the gauge and blow thru the common pigtail to see if it is open.
    Don't have to unscrew/unwire the control that way.
  • lmoore8lmoore8 Member Posts: 13
    I couldn’t get the hex head for calibration to turn. I bent the 1/32” Allen key and it still didn’t move. I had a little more I could wind out the screw on the main/cut in setting (even though the slider was bottomed out) so I’m giving that a try. If that doesn’t work, I’ll just get a new one.
  • BobCBobC Member Posts: 5,101
    A little heat on that allen screw might help. I would use a soldering iron with a chisel tip not a torch.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • FredFred Member Posts: 8,418
    lmoore8 said:

    I couldn’t get the hex head for calibration to turn. I bent the 1/32” Allen key and it still didn’t move. I had a little more I could wind out the screw on the main/cut in setting (even though the slider was bottomed out) so I’m giving that a try. If that doesn’t work, I’ll just get a new one.

    What @BobC said. Use a soldering iron to heat the red or blue locktite around the hex screw.
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