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Pressuretrol and Thermostat

I am a newbie when it comes to steam. I recently tried to adjust my pressuretrol, on the advice of Dan Holohan's book, to a cut in of 0.5 psi with a differential of 1 psi. It's an additive pressuretrol. The settings were reversed before I changed them, i.e. cut in of 1 and diff.of 0.5.

Could this affect the behavior of the burner and the thermostat? I noticed that the thermostat was reading "heat on" while the flame is off. Is this normal? Perhaps I don't understand cycles per hour that well. If it is set for 1 cycle per hour, say, and the temp falls below set point a second time during that hour, does the burner not fire? I'm trying to understand why I'd see "heat on" when there is no flame. Is this normal?


  • Paul S_3
    Paul S_3 Member Posts: 1,257
    edited March 2016
    If all the pipes were hot and the radiators too....it probably tripped on the pressuretrol meaning the pressure in the system reach the cutout setting (1.5psi)....it should maintain in your case between .5psi and 1.5psi.....so to answer your question it is normal for your thermostat to say heat on and the boiler be off....
    ASM Mechanical Company
    Located in Staten Island NY
    Servicing all 5 boroughs of NYC.
    [email protected]
  • BobC
    BobC Member Posts: 5,410
    If the pressure reaches the high trip point the boiler will shut down till the pressure drops down to the low set point. The stock 30 PSI gauge is pretty useless on modern steam boilers but regulations require it. Note that pressuretrols are not accurate at the low end of their range.

    If you had an additional 0-3 PSI gauge you would know what pressure the boiler is actually running at.Then you could easily tell if the boiler was tripped out on pressure. You can see the 3 PSI gauge I added next to the Vaporstat, the stock 0-30 PSI is in the boiler below the Vaporstat and is really just for show.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • jmob77
    jmob77 Member Posts: 39
    Interesting. My 30psi gauge usually reads around 2psi or just above, which seems odd given my pressuretrol settings. Not so accurate, huh?
  • Big Ed_4
    Big Ed_4 Member Posts: 2,373
    The pressuretrol and the gauge are both out of range for what is needed .. If the house temperature drop to much in it's cycle , First clean the pressuretrol's pig tail . Still the same problem bring settings up a tad until it cycles properly .
    I have enough experience to know , that I dont know it all
  • jmob77
    jmob77 Member Posts: 39
    Suddenly getting a lot of short-cycling, starting this weekend. Boiler fired only when I nudged the cut-in pressure up a hair. As soon as I inserted the screwdriver, basically, the burner came on. I need to work on venting my mains; going to check the one that is visible, the other main vent is presumably enclosed in some basement ceiling work done by the previous owner. Is there anything else I should try short-term? If I can avoid it, I'd rather not mess with the pigtail until the Spring weather comes in earnest, plus I've never done that before.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,373
    Raise the pressuretrol up an tad ...

    I have enough experience to know , that I dont know it all
  • Fred
    Fred Member Posts: 8,541
    If you want to fix this, clean the pigtail. It's not a big job and we still have a good month of potential for the weather to get really cold. Take advantage of one of the warmer days and get her done. The pressure is being trapped after the clog in the pigtail, on the Pressuretrol side of the pigtail.
  • jmob77
    jmob77 Member Posts: 39
    What is the safest way to ensure the power to the pressuretrol is off before removing it.? My service panel isn't labeled. In the boiler room, I have two switches marked "clock" and "burner" respectively leading to a step-down trans, then some bx that connects over the the p-trol and other control stuff on the boiler. Do all of those things run on 24V?
  • Fred
    Fred Member Posts: 8,541
    If you aren't sure what the "clock switch goes to, the safest thing to do is turn both of those switches off while you are taking the Pressuretrol off and cleaning it.
    JUGHNE Member Posts: 10,791
    Just to jump in and add a work of caution: to remove the pressure control from the pigtail it must be unscrewed with a wrench on the bottom fitting. This may seem obvious but one poster here removed the 4 screws from the bottom of a new pressuretrol and now has another 2nd new one........The wiring must be disconnected and the entire control unscrewed from the pigtail. Look in the bottom of the control for sludge plugging the pin hole into the control. carefully clean it out plus the pigtail itself. With the control off the pigtail you should be able to freely blow down into the boiler thru the pigtail. Just clean until you have a free passage into the boiler.
    Add water to the pigtail for priming before installing the control back on.
  • vaporvac
    vaporvac Member Posts: 1,520
    You might also use a small union to make cleaning it out easier in the future
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF