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Vaporstat and Pressuretrol wired in series behaving oddly

My new boiler has a vaporstat and Pressuretrol wired in series but they don't seem to be working correctly. The vaporstat has been set to cut out at 1 and 1/2 PSI but it only cuts out at about 4 PSI. The Pressuretrol is also set to cut out out at 1 and 1/2 PSI but it cuts out at about 5 PSI. So far the repairman has been flummoxed and interventions resulted in the boiler temporarily refusing to fire-up. Could this be a wiring, voltage or amperage problem? Does polarity make any difference? I thought at first it must be a bad Vaporstat but when I saw the Pressuretrol having a similar problem it didn't seem likely that both new units were faulty. It's a Weil McClain EGH-85 boiler with an automatic damper, probe water sensor, automatic water feeder and a rather simple but programable digital thermostat. Any ideas?


  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    edited December 2022
    They are each just simple switches, so the polarity doesn't matter.

    You can jump across one at a time to see how the behavior changes (only under direct boiler supervision!!)

    You can use a continuity tester or multimeter to see if each of them is closed when the boiler isn't firing (they should be).

    Honestly if your repairman is flummoxed by these simple basic controls, start looking for a new one (repair tech, not controls)
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    What gauge are you using to verify the operating pressure? If it's the 0 to 30 psi gauge, it's useless. T a 0 to 5 psi gauge into the same pigtail as the vapourstat and see what's really happening.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EStark
    EStark Member Posts: 18
    I'd would check the gauge, also a side question the 0 to 30 is required by code but would a say -15 to 50 still be as it would still read the 0-30 range or does it have to be a 0-30 no matter what? Hence having to tee the line and add the low pressure gauge 
    EBEBRATT-Ed Member Posts: 15,513
    In this instance you are using the pressure control as a high limit and the vapor stat is your operating control. They should be wired in "series". The pressure control should be set higher than the vapor stat set it (pressure control) to cut out a 4 psi with a 1 psi differential to keep it "out of the picture" you don't want it interfering with the vapor stat operation in this instance it is serving as a high limit back up control.

    Then set the vaporstat to operate the boiler at the pressures you need and let it run the boiler. The pressure control should serve as a back up control that will only shut the boiler down if the vaporstat fails
  • neilc
    neilc Member Posts: 2,702
    we have a first time poster here,
    chasing pressure questions,
    and nobody wants to mention pigtails, or pictures?

    do you know if repair man checked your pigtail(s)?
    the looped pipe under the Ptrol and Vstat?
    they clog up and don't allow the pressure controls see what's happening in your boiler,

    and we love pictures,
    let's start with the Ptrol and Vstat, and the pigtail(s),
    all in one shot if you can,
    add the sightglass and we'll see what we see,

    as for the wiring,
    you can try removing one wire from one of the controls, and see if the boiler will fire,
    (turn up the thermostat, it should not fire with 1 wire removed),
    then put that wire back, and remove one from the other control,
    again, boiler should not fire,
    turn off the service safety switch on the boiler while wiring and unwiring,
    back on for the testing,
    known to beat dead horses
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,897
    Not sure thats the best set up for your needs..  The guys are right in things to check and you should post pictures.   I've always used a Vaporstat or Regular P-Trol and a manual reset Pressuretrol in series even on commercial boilers.  On some really large commercial steamers it gets a little fancier.  Make sure you are using the right vaporstat.  One model goes up to 4 psi and the other only goes up to a lb. 16 ounces (thats what I put on my Vapor system which shuts off on 12-14 ounces)  of course, I have the BEST ones...with Mercury.  Sooooo accurate!  The non-mercury P trols and Vaporstata ARE NOT the same.  I've seen them bad right out of the box and shot after one year.   I always save the old type off of boilers were ripping out...same w T Stats.   Mad Dog
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,897
    Oh....sorry. guages.  I've used Weksler (Me thinks they are still on Long Island) gauges...liquid filled, well made and accurate.  They make all kinds of pressure increments.  I like ones that read in ounces.  The only way to truly dial in the right operating parameters.  Mad Dog
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,897
    This is on my antique  Vapor system. Its probably 125-140 years old .  
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,897
    I took it off an ancient vapor system in a huge Long Island Gold Coast Mansion in Old Westbury.  Its still works perfectly.  Mad Dog