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Short Cycling - do I have it, should I care?

My Weil-Mclain EG75 (2 pipe steam boiler) cuts off at 2lbs and cuts on at 1lb.  This is as low a pressure as I can seem to get with the P-trol I have.  My understanding is that lower is better.

When the system is running, (not from a <span style="text-decoration:underline;">cold</span> start) it takes about 2 minutes from the "cut off" (at 2lbs) for it to drop down to 1lb., and restart.  It then takes about 2 minutes for the pressure to climb <strong>back</strong> to the 2lbs cut-off point and shut off again.  This seems to be the cycle it follows until the thermostat is satisfied.  Is this OK, or is this short-cycling?  Anything about this I need to be concerned about? 

By the way, from a <span style="text-decoration:underline;">cold</span> start, it take about 20 minutes of running to reach the 2 lb cut off point.

Comments

  • Dave in QCA
    Dave in QCA Member Posts: 1,764
    Not Short Cycling

    When the system comes up to the cutout pressure, it usually does not take very long for it to drop after the burner shuts off, and likewise, after it restarts, it will build pressure pretty quickly because the system is already hot.  This is not harmful.



    Does this occur frequently, or only when coming out of a temperuature setback?



    It does sound perhaps, like your boiler may be a bit oversized.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
    http://grandviewdavenport.com
  • Kentucky_Steam
    Kentucky_Steam Member Posts: 26
    Might be oversized...

    Two or three contractors proposed at WM EG65, but I got a real deal (seriously) on a 1 year old EG75 that I just could not pass up, so yeah, I might have an oversized boiler for the house.

    The 20 minutes "warm up" time is after a set-back period.  However, once those 20 minutes have elapsed, it runs, shuts down for 2 minutes, rests for 2 minutes then fires and runs for 2 minutes until my cut-out pressure is reached.  This goes on until Mr. Thermostat is satisfied.
  • Jamie Hall
    Jamie Hall Member Posts: 15,858
    As Dave says...

    not to worry -- this is quite normal.  Your boiler probably is a little oversize, though, and you might enquire of your technician if it is feasible to down fire it slightly...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Kentucky_Steam
    Kentucky_Steam Member Posts: 26
    Just one more question....

    Once in a while (that means I'm not certain when this occurs), I'll be in the basement and hear the Main Vent sucking air in...?  The boiler isn't firing at this time and it may be after a heating cycle and the thermostat is satisfied.

    It sounds as though the Main Vent is actually drawing air in.  If I look at the pressure gauge, it will a slight vacuum situation, that is... it's below 0 pounds on the dial.  Is this normal?  Does that vent "breathe in" sometimes, or is the vent stuck open.  I thought these guys blew cool air out of the way and then shut.

    Any thoughts here....
  • Dave in QCA
    Dave in QCA Member Posts: 1,764
    edited March 2011
    This is Normal

    The vents allow the air to leave, when the boiler is just starting to make steam.  As the steam heads down the pipe, the vent lets the air out.  When steam gets to the vent it closes. 

    Then, when the boiler shuts off, the steam in the system condenses to water.  This creates a vacuum, and the vents allow air to go back into the system.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
    http://grandviewdavenport.com
  • Kentucky_Steam
    Kentucky_Steam Member Posts: 26
    Thanks for the reassurance...

    The house is 100 years old and we've lived here for 33+ years.  The older boiler that we removed was (I think) original to the house - that's before the Titanic was put into service.  It had no LWCO or water feeder except for me (the vigilant home owner).  My point being, having this "new technology" in the basement offers me an opportunity to ask these kinds of questions, and I appreciate having this resource (The Wall) to post questions.  Thanks for your guidance.

    My wife calls the basement my "man cave" since I spend so much time down there learning about how my new toy works.
  • Dave in QCA
    Dave in QCA Member Posts: 1,764
    A Properly Maintained Boiler Room....

    Should never be used for storage.  It should be kept clean and free of clutter. 

    The only items that should be present in a properly maintained boiler room is a comfortable old chair, a small fridge so that refreshements are within reach, and perhaps a TV or small stereo.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
    http://grandviewdavenport.com
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