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vapor stat on a short cycle

nsale Member Posts: 2
Hi, I just switch my honeywell pressuretrol for a Vaporstat. With the Pressuretrol all my radiator were banging now with the vapor stat they are very quiet. The only problem is that the vapor stat is running on a very short cycle. My system is fairly new and the boiler is equipped with a 2 stage gas valve.
Any ideas?


  • KC_Jones
    KC_Jones Member Posts: 5,082
    You are running at a lower pressure now, if the boiler is oversized, or poor venting, or both this would be expected performance. This is why sizing and venting are so important on a steam boiler.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • nsale
    nsale Member Posts: 2
    I had my boiler maintain 1 month ago. The system was fairly balance with just a little bit of banging. The guy put some Steam Boiler Cleaner/Inhibitor and since then a lot of air was going out of the vents and a lot of banging start. All the radiators are tilted on the right position.
    so I decided to change my pressuretrol for a vapor stat.
  • Jamie Hall
    Jamie Hall Member Posts: 18,962
    First, get the steam boiler cleaner and inhibitor out of there. You need to drain the boiler and refill with just plain vanilla water. If your water is very acid -- pH less than 6 -- you might want to put a little bit of Steamaster in there. Just a little.

    Next, what do you have -- if anything -- for main venting? If the vapourstat shuts off the boiler before some of the radiators have started to get warm, you will need more main venting -- whether the boiler is oversized or not.

    Now things get a little more complicated, and you really need to have a low pressure gauge (0 to 3 psi) on there to see what's happening. Is the two stage gas valve connected to operater? If so, it should drop to low fire at slightly less than 8 ounces per square inch -- less if you have a two pipe vapour steam system -- and shut off completely at perhaps 1 to 1.5 psi for a conventional two pipe or one pipe system (vapour systems are a little different). Then, as the pressure drops, the low fire should come back on somewhere between the cutoff and that 8 ounce figure. High fire should come back on -- if the thermostat is still calling -- at perhaps 4 ounces. But, as you can see, you need that low pressure gauge to see what's happening.

    And don't even worry about the pressures until you get the venting all nicely done.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 12,014

    What controls your lo-hi fire? Are you able to run the boiler lo-hi-off with the controls you have?

    You need at least two controls. 1 runs lo hi fire and one limit to shut you off on high pressure