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High Water Cutoff for residential steam boiler?

Dave_12 Member Posts: 77
Working with a contractor who is starting to service an existing job. A 245 MBH input package steam boiler serving one pipe steam. A 20 gallon boiler feed system with a 1/3 HP pump is in place controlled by a MM 150S Pump Control. There are master traps on the returns. The boiler appears reasonable well piped (both risers from boiler used with acceptable rise, header and equalizer per mfg spec etc).

I am suggesting changing to a 42S or a 150S-MD pump control as being more appropriate, and installing a globe valve on the pump discharge to throttle it down (not one existing). Also suggest adding a probe type manual reset LWCO. We don't have history of installation to know why the boiler feed system was installed so I can't question the need for it.

More then once the system has overfilled, causing water to spit from the radiator air vents. Someone installed a MM 64 for use as a high water cutoff but the overfilling has still occurred. Currently this 64 is installed in the line with the 150S - hopefully the attached picture shows this. Not sure yet on how the 64 is actually wired and if will kill the feed pump or not, so not really sure as to what has caused these overfilling events.

Homeowner wants to prevent the overfilling again so a HWCO needs to remain. Looking for advise on if the 64 HWCO should be in the same vertical pipe as the LWCO or if it should be moved? Should a quick-hookup fitting be used to tie the LWCO in with the gauge glass. How would you wire a HWCO - kill the boiler and the feed pump? Any other thoughts on the installation?


Brant Wininger
Cody Sales & Engineering


    JUGHNE Member Posts: 11,074
    Do I understand correctly that this is a 245,000 BTUH input boiler?
    If so, it looks like a relatively small boiler for 1 pipe steam really got dressed up with accessories.
    Does all the return water go into the feed pump? (I have seen that not happen and produce high water levels.)
    Where does the feed water pump connect to the boiler for feeding?
    Do you have, in effect, 2 equalizers connected to the header?
    More pictures from farther back would be very interesting.

    Where are you located?
  • Jamie Hall
    Jamie Hall Member Posts: 23,428
    What controls the feedwater pump? It should be controlled soiely by low water in the boiler. Nothing -- repeat, nothing -- else. Provide an overflow -- which can be monitored -- on the tank. You should also have a float valve on the tank to fill that if it gets too low.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,074
    If the wet pipe under the LWCO was partially plugged the water level could be sluggish to move correctly. Level drops and not raise with pump running and that could over fill.
    IIWM I would clean all the piping for controls & sight glass.

    The returns might have been slow and the feeder was added?