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Pressuretrol Not Working??

I have a single pipe steam boiler system. Based on advice that I saw on this pipe I set the cut-in and cut-out to the lowest possible settings, i.e. cut in at 0.5 and cutout at 1.5.

In the past, when I observed the boiler, the pressuretrol always seemed to be doing its job. After a few minutes of the boiler firing, the pressuretrol would kick in and shut down the boiler for a few minutes before it turns on again.

The last few days have been unusually cold here in New York and my boiler is on a majority of the time. But for some strange reason I don't observe the pressuretrol kicking in any more. It seems to me that any time the thermostat calls for heat, the boiler is firing. This has me concerned that maybe the pressuretrol has gone bad and my system is working on too high a steam pressure.

When I look at the pressure gauge, however, it is not showing a high reading. In fact the needle barely moves off of the lowest setting.

My question is: could there be an "innocent" reason why pressure is not building up inside of the boiler, or is something most likely wrong with the pressuretrol?

could it have something to do with the water level in the boiler; is a high or low water level likely to have an affect on the pressuretrol?

or could it have something to do that the boiler is on so much and hence there is less air trapped in the radiators and perhaps less pressure as a result?

I realize that every boiler is different, but generally speaking how long should a boiler be firing on average before the pressuretrol shuts it down?

Any tips would be appreciated as I would like to be rest assured that everything is ok with the boiler and it is not running at too high a pressure. Thanks!


  • Fred
    Fred Member Posts: 8,542
    You need to put a 0 -3 PSI Pressure gauge on the boiler along with the 0 - 30 PSI Gauge that's on there. That's the only real way to answer your question. The standard 0 - 30 PSI gauge just isn't accurate enough to see actual pressures in the lower ranges. If your boiler is properly sized to the connected radiation, it may never build pressure. That is exactly what you want and the Pressuretrol is there only as a Safety device.
  • Jamie Hall
    Jamie Hall Member Posts: 22,889
    And the fact that under more normal conditions it "kicks in after a few minutes of boiler firing" suggests strongly to me that you need more main venting. Probably a lot more main venting...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • wanttolearn
    wanttolearn Member Posts: 59
    I am confused by your responses. Based on everything i read in the past I thought that in a normal steam boiler it is supposed to keep shutting on and off as it builds pressure and the pressuretrol kicks in. Your responses imply that the pressuretrol should normally NOT kick in unless there is a problem. so in a properly sized system is it normal for a boiler to fire for 20 minutes or so without the pressuretrol kicking in?
  • KC_Jones
    KC_Jones Member Posts: 5,691
    If the system is sized properly the pressuretrol should never activate. The pressuretrol is a safety device not an operating control.

    There are many systems it is an operating control, but that in general is due to improper sizing or installation. With a boiler sized to the radiation the radiation can condense the steam at pretty much the rate of production. In a perfect world it could, in theory, fire forever and not make any real pressure.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • Fred
    Fred Member Posts: 8,542
    @wanttolearn , What we have always tried to say is that rather than let a boiler build pressures well beyond what is reasonable, the Pressuretol must function to control that. If the Boiler never builds pressure, then the Pressuretrol is there only as a safe guard to prevent some abnormal/unusual event.
    -If the boiler is sized to match the connected radiation, pressure won't build enough to trip the Pressuretrol. Changing the settings like you did should not have an impact on when the Pressuretrol trips.
    - If the boiler used to trip the Pressuretrol at a higher Cut-in and Cut-Out setting and now it doesn't, at the lower settings, then something else may be going on that may be allowing steam to escape, maybe a hole in the top of the boiler or leak elsewhere?
  • Jamie Hall
    Jamie Hall Member Posts: 22,889
    Just to give you an idea, @wanttolearn , the system in the main property which I superintend has a vapourstat, set to cutout at 7 ounces per square inch (not pounds, ounces). When maintaining a constant differential of 70 degrees between inside and outside, like today, it will normally run about 30 minutes -- and never cut out.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Neild5
    Neild5 Member Posts: 163
    We lost power with it 10 degrees outside and when it came back on the boiler ran for almost an hour and the pressure never went over 0.25 psi to heat a 20 unit condo building.
  • BobC
    BobC Member Posts: 5,471
    The boiler may just be responding to it's environment. It may be the extreme cold is causing the steam to condense faster so you just may not be able to build pressure the way you would if it were 30 degrees outside.

    If your boiler is rated to deliver 280 sq ft of steam and you have 230 sq ft of radiation I would expect it might cycle because of building pressure but remember the radiation number assumes an environment of 70F. If all the piping in the exterior walls and radiators on exterior walls are cooler the effective EDR is higher so the boiler may not cycle as much.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge