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Steam Pressuretrol Confusion

Hi All. I have a steam/gas system heating a four-story townhouse. After reading that my pressuretrol is supposed to be set to cut in around 1, and cut out around 3, I looked at how mine were set up. I was hoping you guys could help me sort things out. I'm attaching photos.

- My gauge reads around 6/7.

- I have two pressuretrols. One is an old 404A, and the second I believe is a new 404A (I don't see a model number). The old one is set to 8/9 Main and 1 Diff. The new one is set to 3 Main and 1 Diff.

- I was thinking that the old one is meant as a high limit cutoff? But as I understand it, the high limit cutoffs are supposed to have a manual reset button, and I don't see that on the 404A.

Does the combination of these two pressuretrol models make sense?

If so, can anyone guide me as to how to bring my pressure down to the appropriate levels?

Thanks in advance!


  • Jamie Hall
    Jamie Hall Member Posts: 17,121
    Oh! Antiques!

    But there's no  reason why they shouldn't work anyway...

    First question, though: does the pressure gauge go to zero when the boiler is off?

    If so, and it reads 7 when the system shuts off, that tells me that the all metal pressuretrol simply isn't working.  There are a number of reasons why it might not be, of which the most common are that the pigtail or the opening from the pigtail to the pressuretrol or the opening from the pigtail to the boiler is clogged.  Or all three.  In any event, it would be worth taking it off and making sure all the passages are clean.  Might as well do that for the plastic covered one, too, while you are at it.

    It could also be that it just isn't working.  In which case, you want to replace it with a nice new one like the plastic covered one you have -- or better yet, replace it with a manual reset type and set that to cutout at 7.

    That done.  You really want your cutout pressure to be more like 2 psi, assuming this is all residential work.  So -- set the existing plastic covered one to cut out at 2 psi, with a 1 psi differential (that one is subtractive).

    Then fire it up and see what happens.  Ideally, the boiler should cut out at 2 and cut back in at 1.  If not, ask again!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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