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Question regarding Pressuretrol

norb Member Posts: 44
I have a Honeywell ( additive) due to the "cut-in" labeling on the outside where the main scale slide is located.

My Question, just to make sure I am understanding how the pressuretrol and the guage ( 0--30psi ) should be working:

     If I set the "cut-in" to 1/2 and on the inside of the pressuretrol I then set the "Differetial" to . let's say' 3 1/2, then is 4 the PSI reading I should have on the guage when the furnace starts to run, based on the call for heat?  Is this correct?

If this thinking is not right, would you explain to me how those settings should work?  My guage needle does not move from the zero ( or I should say one psi marker on the guage).   If my psi should be 4 on the gauge but the guage does not move, is the guage faulty or the piping blocked around the gauge?


  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,849
    Cut-in plus differential equals cut-out.

    You won't have any pressure in the system at all when it starts up. (If the gauge isn't reading zero, the gauge isn't accurate.) The pressure builds as the steam is generated and expands into the risers and mains. Ideally, the vents at the ends of the mains should allow the air to escape without building a significant amount of pressure. This allows the mains to fill with steam quickly.

    The pressuretrol interrupts current to the gas valve when the pressure reaches the cut-out point. This causes the pressure to fall. When the pressure falls to the cut-in point, the pressuretrol closes and heating is resumed. This off-on cycle is referred to as cycling on pressure, and the pressure range in which this occurs corresponds to the pressuretrol's differential.

    If you have the cut-in set to .5 and the differential set to 3.5, then 4 psi is the cut-out, or the point at which the burners will be turned off.

    If your gauge never moves, this can have two possible causes: either the gauge is bad or the system is not cycling on pressure. It is not only possible but desirable to get steam to all the radiators, heat the living space to a comfortable level, and satisfy the thermostat, without ever cycling on pressure. Unfortunately, if you can't rule out both the pressuretrol and the gauge being blocked, it will be difficult to tell without removing the pressuretrol and seeing if you can blow air through the pigtail.
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • David Nadle
    David Nadle Member Posts: 624
    It's normal.

    Especially now when it's not that cold, it's probable your system is not exceeding 1 PSI, and it's normal for the 30 PSI gauge to not register such low pressures. To see fine pressure changes below 3 PSI you need a more sensitive gauge. I think you should try setting the differential to 1.
  • norb
    norb Member Posts: 44

    thanks for the reply
This discussion has been closed.