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Vapor Steam System Short-Cycling

We replaced a 68 series with an ECT5 firing 1.35 g.p.h. This boiler is 6" taller but we met the minimum requirement of the mfr by having over 24" from water line to header.

We have a customer who sits by the boiler with a notepad and watch and says it is short-cycling. He says sometimes it's fine and others it isn't.

The original 1928 #6 Hoffman vent is still in the system.

Right now we are running with a pressuretrol at 1/2lb. The previous systerm was running with a presuretrol. Our supplier has suggested exchanging pressuretrol for a vaporstat.

The house is approximately 3,000 sq.ft. and all radiators have vapor traps at the bottom.

Any help would be greatly appreciated.


  • ChrisJ
    ChrisJ Member Posts: 14,967
    edited February 2012

    What type and size header did you use?  How many and what size risers out of the boiler?

    I almost forgot,  What kind of LWCO does it have?  Is it a Hydrolevel Cycleguard by any chance?
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Dave in QCA
    Dave in QCA Member Posts: 1,777
    Short cycling or Short cycling?

    When the owner says it's short cycling, is this only after the system has run for a period of time and all of the radiators are fully heated, or is this occuring during the heating up process?

    It sounds like some improvement in venting may be in order as the old vents on the mains were generally not fast enough.

    A vapor stat is always a better control, but chances are if this system is building pressure and you set the vapor stat in 8-16 oz, where it should be, you will have even more short cycling.  It all depends.  If the short cycling only occurs after the system is fully heated, you might be able to down fire the burner a bit.  However, i would make sure that the owner has all the radiators on and that they are all heating and fully heated before the short cycling begins before I would make any changes.

    If the Short cycling is happening during the heating up stages, it is likely the main vent (s) are too small or are not working correctly.
    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.
  • crash2009
    crash2009 Member Posts: 1,484
    edited February 2012
    Put a data logger

     on it for a few days.  You will know for sure what its doing.  http://www.testequipmentdepot.com/lascar/dataloggers/elusbtc.htm
  • Jamie Hall
    Jamie Hall Member Posts: 21,568
    to all of which...

    I would only add that "short cycling", if it is happening towards the end of a long heating cycle -- as Dave says, when everything is nice and warm -- is, as a general thing, normal, since there needs to be extra capacity in the boiler to get things up to speed but then there is more capacity than needed.

    If it is worse than two thirds on and one third off, you could try down firing (if, as Dave says, everything is open now).

    The real problem here is that, if it is at the end of a cycle, it is normal -- but you may have the dickens of a time convincing your customer of that.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • elfie
    elfie Member Posts: 266
    data logger - how configured to monitor steam cycles

    have a couple date loggers (a wonderful device for about $100)

    how do you set it up to monitor steam cycles?

  • crash2009
    crash2009 Member Posts: 1,484
    The model above

     comes with a thermocouple/temperature probe.  All I did was jam the probe in a crack in the mortar between the chimney and the flue. 
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