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Pressuretrol set correctly but not cutting in/out proprely

I've got a bit of a weird situation,  20 year old Weil McLain gas fired residential boiler. This year I started to notice that my cycles were longer than normal, vents were failing and water hammer was more prevalent. Pressuretrol is set properly with 0.5 and 1 as always but I am hitting 2.5-3psi before the boiler cuts in. My pigtail is clean so I replaced the pressuretrol and the same issue is occurring. 3rd pressuretrol has not solved the issue so I'm assuming it's not that!

Nothing else has changed from years past. My system is now loud as can be, I'm going through vents at a rapid rate, I'm making wet steam because of the higher pressure, and I assume I'm spending more money on gas.

So if its not the pressuretrol, pigtail or pressure gauge, does anyone have any ideas on what the heck is going on with my system? Thanks!


  • MTCMTC Member Posts: 181
    Just to clarify...

    you're cutting IN at 2.5-3PSI? Or is that when it cuts OUT? Whichever it is, what pressure is the other at?

    Are you sure your gauge is working properly, and that its pigtail is clear of junk? Are the pigtails primed, to prevent junk/steam from getting to the controls?
  • Correction

    Sorry MTC I meant to say cut OUT. Cutting back in occurs around 1.5. It's like the system is just adding 1 to all my settings. And yes, the pigtail is clear. My plumber swapped out my 0-30 gauge for his 0-5 just to make sure I was getting the proper readings, and both had the same figures. I trust my plumber when it comes to steam and this one has us both confused.
  • Jamie HallJamie Hall Member Posts: 6,701
    edited February 2013

    Pressurestats can get out of calibration.  I you have a really reliable pressure gauge, you could try recalibrating the 'stat.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • MTCMTC Member Posts: 181
    I don't think it would be calibration

    if the OP did in fact try 3 different Pressuretrols on the boiler with similar results, unless something is really screwy with a batch of Honeywells...
  • Jamie HallJamie Hall Member Posts: 6,701

    misread.  Where are my bifocals?  But it still seems odd to me that the OP should have a constant offset between three pressuretrols on the one hand and a gauge on the other...

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • MTCMTC Member Posts: 181
    Can you post pictures...

    you never know what random thing we might see in a picture.

    One thought, you said "my pigtail is clean," does this imply that the gauge and pressuretrol share one pigtail? Even if that's unrelated to your current issue, you'd be better off having each control on its own pigtail.

    I was just trying to think through how something could be off and keep having the same effect on both the pressuretrol and gauge with different pressuretrols and gauges. It doesn't make much sense to me that a shared pigtail would give the effects you are describing, but it would be a common link. That or some sort of obstruction in the line going back into the boiler, would be potential shared influences on both control and gauge...

    Just thinking out loud, hoping someone more experienced than me will come up with something actually brilliant :-P
  • Charlie from wmassCharlie from wmass Member Posts: 3,922
    I would check

    the boiler tapping the pigtail goes into. Also check the tappings for your site glass. Photos always help.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • J.A.J.A. Member Posts: 18
    Gray Pressuretrols

    If you have the gray box pressuretrol, that is probably your problem. Those things are junk and do not accurately control the pressure. If your system is well vented at the mains and radiators it is filling with steam quite quickly. What you want to do, in order to run your system in ounces of pressure, is get a vaporstat. You'll probably find you don't need anything more than half a pound limit (8oz) with a cutout of 4-6oz (vaporstats are subtractive) Oddly enough both are made by Honeywell, but the gray boxes just are not made to accurately handle low pressure whereas the vaporstats are fantastic and handle very low pressures which is what you want.
  • Pic attached

    Please see attached for a pic of my pigtail. And I know some people don't like the cheap Honeywell pressuretrols, but I can't believe it's the pressuretrol(3 of them) that is causing this.
  • J.A.J.A. Member Posts: 18
    Gray Devil

    That's him right there, the little gray devil. I also questioned whether or not that could be the problem on my system and tried 3 others as well. In fact, someone from this Wall who lived nearby came by with two of his own to try out and they all had the same result. They're all made the same way and do the same thing, they don't handle very low pressure which is what you really want in a residential steam system. I ended up with the 1-4lbs Honeywell Vaporstat and it's set at 1/2lbs with the differential at 4oz. When I first installed it I was amazed at what a difference I heard and saw.

    I remember a little while back, I think it was Gerry Gill, who posted his experiment with testing those Gray boxes because he too suspected their (in)ability to properly operate at their stated pressure. You can find that test with a search here on the site. I'm usually just a lurker on this site so apologies if I am mis-remembering who performed the tests.

    In re-reading your original post, you mentioned that you noticed longer than normal cycles. That would not be something controlled by the pressuretrol, so you should make sure the settings on your thermostat are correct. If they are fine and you are purely concerned with the pressure, a vaporstat is the way to go.
  • Thanks JA

    I think my longer cycle times are a bit longer simply because the cut out is happening later in the cycle. Might just be psychological as I used to hit temp in years past on cold nights after cut out but before cut back in. Now my boiler runs to 2.5 and cuts out pretty much exactly at the same time the temp is satisfied.

    I know I read somewhere that the boiler operates most efficiently when the pressure is low, but I'm not an expert so I don't know if running around just under 2.5 is that much more inefficient that running between 0-1.
  • J.A.J.A. Member Posts: 18
    An expert's help

    Might I suggest picking up Dan's book We Got Steam Heat you can get it here

    That book is filled with all sorts of information that will help you understand your system better. It will also explain much better than I can in a few sentences why you want low pressure in your system. Anyone on here will tell you it is a very quick read and worth its weight in gold.
  • MTCMTC Member Posts: 181
    edited February 2013
    $160 or so

    for a vaporstat might be a worthwhile investment anyway, even if it doesn't solve your problem directly. The whole system works better on low pressure, lower than a pressuretrol that is operating correctly can even possibly provide.

    If the cutout has increased to 2.5 from a lower cutout, then yes your cycle time would be longer... often it takes a few cycles on pressure to satisfy the thermostat, so the pressuretrol would be the culprit to a longer cycle time, as it takes longer to build 2.5PSI than it does to build 1.5PSI or whatever it used to cut out at.

    If you do decide to get one, try a starting setting of 10oz cut-out, with 6oz differential (vaporstats are usually subtractive, so that gives you a cut-in of 4oz. This setup usually works well with most smaller systems. YMMV.
  • blakkblakk Member Posts: 3
    Burnham Gas Fired One Pipe Steam System Pressuretrol Problems

    I have a brand new Burnham Gas Fired Steam Boiler on a One Pipe Steam System. It has a Honeywell Pressuretrol high psi cutoff unit that does not do its job!

    It does not shut off at the set high limmit...It pushes water up into the pipes until the water in the site glass is almost below the low water cutoff. IF I tap the top of the box with a hard object, then it shuts off....if not the pressure just keeps rising! WHY?

    I ordered a "VAPORSTAT L408J1017" to replace the crap ass Pressuretrol...Will this solve my problem?
  • BobCBobC Member Posts: 4,449
    Bad control

    You may have a sticky microswitch in that pressuretrol or sticky linkage. What pressure does the gauge read just before you tap the pressuretrol and what is the pressuretrol set to?

    Let us know if the vaporstat does not correct the problem and start a new thread if you still have problems.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • blakkblakk Member Posts: 3
    edited February 2013
    Burnham Gas Fired One Pipe Steam System Pressuretrol Problems

    I bought the Vaporstat L408J1017 and it shuts off exactly where I set It. Way better than

    the pressuretrol. The problem is I don"t know how to set the differential versus the MAIN setting? So It keeps cycling off and on....As soon as the pressure drops below the MAIN setting it kicks back on. I know it"s subtractive but the MAIN is graduated in Psi but the DIFF is in kpa and OZ In2.

    Anyway advice would be greatly appreciated!

    Thank You
  • MTCMTC Member Posts: 181
    edited February 2013
    Setting the vaporstat

    Vaporstats are subtractive, as you mentioned. So the main is the cut-out, you subtract the differential from the main, and that is your cut in.

    For most residential boilers, a good starting point is 10oz main, 6oz differential (so you cut in at 4oz). Many people on here go lower than that, running at more like 2-8oz.

    If you're cycling on and off very quickly, you probably need better main venting, and possibly some radiator vent attention too (if its one pipe) or steam trap work (on two pipe).

    EDIT: I see you said you're on one pipe, sorry, read too fast. If you're still having trouble after this, as Bob said, please start a new thread and explain your problems, with pictures of your system for us to look at.
This discussion has been closed.


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