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Steam Boiler Pressuretrol wont cut in/out.

Danthalas Member Posts: 2
Hey guys ,

I have a crown steam boiler 1 pipe system. For some reason the PSI gauge reaches 15 and my relief valve opens and releases steam due to overpressure.
I had a technician come in and said the pressuretrol is workimg fine and did some troubleshooting and didnt find a reason and just basically told me to get a new boiler. obviously he doesnt know his craft and trying to get me to spend money that i don't have .
Now , ima a former US navy boiler tech machinist mate, so im familiar with how steam systems work. From doing some research on this forum and HVaC talk there was some possible reasons but none checked out.
1. pigtail could be clogged ? Based on people advice if my PSI gauge is working then the pigtail is working correctly, is that correct ?
2. Pressuretrol died ? ive read pressuretrol usually last a long time.
3. Pressuretrol are usually flaky on low psi settings
4. My pressuretrol is SUBTRACTIVE : setrings are Main : 2psi & Differential : 1.5 is this setting reccomended ?

Any advice or troubleshooting help will be greatly appreciated.


  • Steamhead
    Steamhead Member Posts: 16,835
    edited January 2020
    Check the pigtail first. If it is clear, replace the pressure control.

    If your boiler has the Honeywell control with a transparent plastic front (L404 I believe) these have been troublesome. Replace it with the PA404A, since this type is more reliable.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    EBEBRATT-Ed Member Posts: 15,524
    Post a few pictures of the pigtail , pressure control etc if you can
  • Danthalas
    Danthalas Member Posts: 2
    ok will post pectires later today
  • ThomasM84
    ThomasM84 Member Posts: 7
    I've been faced with this situation before and for me it was the pigtail that caused the entire hassle. Did you figure out what the issue was in the end?
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,006
    The two L404s with ranges 15 psig and lower are both subtractive and the minimum operating range is 2 - 15, with a subrtactive differential of 2 - 6 psig. I believe this means the cut out has to be more than 2 psig, otherwise the thing doesn't work.

    There are comments in discussions and references about trying to operate nominally at 0.5 cut in and 2.0 or less cut out.

    What am I missing?

    I just installed a new Pressuretrol PA404A1033 and with the cut in set at 0.5 and the differential at 1.0 from the factory, it cuts out at 2.7 psig and cuts in at 0.7 psig (using a 0-5 psig gauge temporarily, because its not per code). I am addressing this issue with Resideo, which has taken over from Honeywell. More to follow in my discussion.
  • Jamie Hall
    Jamie Hall Member Posts: 23,286
    It should be possible to set the L404F1060 to cut out at a bit less than 2 psi, although nominally the minimum cutout is 2. The differential can be set a bit lower than 2 also -- so it should work. Your PA404A should work as advertised -- that it does not seem to suggests very much that it needs to be calibrated; most of them seem to. The pressuretrols have a smaller diaphragm than the vapourstats, which is how the vapourstats can be set to lower (like much lower) pressures, and are more accurate and more repeatable. And cost more...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,006
    Nice try, but I doubt the cut-out minus differential can be set at 0.5 psig. That's a bit far down the scale.

    I did get an email from a Resideo product manager late last week and replied over the weekend. No followup from him so far.

    Time will tell.