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Update: Curious about Cause of Flooded Steam Boiler

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Follow up:

We received another no heat call, and again the pump was running. The boiler was also flooded again. I carefully removed the cover of the MM150S level control. I found that the float was up and the lever of the switch was completely depressed. A small bump to the switch and the pump stopped. We replaced the head of the MM150S and all is well again.


  • Jamie HallJamie Hall Member Posts: 13,416
    Thank you for the update -- always useful! And nothing like a stuck switch...
    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
  • ttekushan_3ttekushan_3 Member Posts: 926
    I've had 4 of them do that in recent years. All on new installs.

    Three heads were replaced under warranty and one replacement failed also. I instructed maintenance staff on the percussive method to get the switch contacts to open. A small rubber mallet or even the ball of the hand can work. And then how best to drain the system.

    Don't ask me how I learned how quickly a couple remote transfer pumps operating simultaneously can flood a boiler feed tank straight up and out of its vent line once the boiler feed is successfully stopped. Especially when you're bent over opening the drain valve!
  • Any good alternatives to using the MM 150S? It sounds like the quality of their controls continues to plummet. The electronic Low water cuts are no longer even carried by the reputable supply houses I work with.
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • ttekushan_3ttekushan_3 Member Posts: 926
    I don't see a viable competitor to the 150. It's such a sensibly designed device and has been a true workhorse in the past.

    To be fair, I don't see any shortcomings in the way they are made today, but I do see a problem with the MicroSwitch brand of switches used internally. Like M-M, MicroSwitch has been around forever and has been a benchmark product in industrial electrics. On the failed units where switches have stuck, the spring tension for the snap action is weak and the "snap" much less distinct than it should be. And this is on a nearly new control. I've seen similar MicroSwitch models on old machine controls feel nearly new in their action despite having 10's of thousands of cycles and decades of use under their belt. Why this cropped up 5 or 6 years ago and apparently remains an issue I don't know.

    And why M-M has not gotten on their case about it I also don't know. I'd hate to think that there's an underlying attitude of "who else ya gonna go to?"
  • BobCBobC Member Posts: 5,128
    The problem is some companies will do ANYTHING to save a penny. In large companies the accountants have a lot more say than the engineers do.

    The attitude that the only that counts is the next quarters profit and loss statement has destroyed a lot of fine old companies.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
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