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Two pipe steam system, boiler flooding

Hello i am having trouble at a job and am hoping someone can help me out. I am dealing with a two pipe steam system. half of the radiators have thermostatic steam traps and other half are gravity. There is a condensate tank next to boiler with a 2" F&T trap. M/M #150 controller on boiler works with condensate pump and there are no coils in boiler. Boiler provides heat only. Everyday the boiler is flooding. I flushed the boiler several times and priming/surging is under control, 150, F&T trap, condensate pump, and air vents on return were all replaced. Control tree, gauge glass, surge columns, etc were all checked and cleared of any blockages. The vaporstat was lowered recently to 1.5 lbs and return lines never get hot. i was able to find some old pictures and discovered what the original setting on the vaporstat was and has been for years and there was never an issue until now. boiler currently cuts out at 4.5 PSI and cuts back in at 3. (I know this is high but this is how this system has been for many years with no problems). I am going back to this job tomorrow to follow up and see if raising pressure helped. Any help with this would be appreciated. Thank you


  • Jamie Hall
    Jamie Hall Member Posts: 17,085
    Gravity? What, exactly, do you mean by a gravity steam radiator?

    But to the flooding problem. Where is the extra water coming from? Is there perhaps an automatic feeder -- float or somesuch -- on the boiler or condensate tank? If the pump is properly connected as a boiler feed pump (that is controlled only by the level in the boiler) it cannot over fill the boiler -- unless there is an independent feed to the boiler. On the other hand, if the condensate pump is controlled by a float in the condensate tank, it can easily do so if the condensate return is inhibited or slow.

    I'm not at all keen on either condensate tanks or F&T traps on residential systems -- they are almost never required, if the steam traps on the rest of the system are working properly and the pressure is kept where it belongs. Therefore... why are they there?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    delta TNew England SteamWorks
  • Danny Scully
    Danny Scully Member Posts: 1,329
    edited March 2018
    I’d love to tell you to throw away the condensate pump (because 9 out of 10 times they aren’t needed) and drop the pressure back down, however, I need to know more about the system. Tell us a bit. Also, in terms of pressure, are you referring to pounds our ounces? A vaporstat operates within ounces.
    New England SteamWorks
  • delta T
    delta T Member Posts: 860
    First rule of steam heating, turning the pressure up will almost never solve a problem, and will make most problems worse. Can you post some pics of the near boiler piping, condesate tank, and also of the 'gravity return' radiators? I have a hunch they may be orificed rads....
    New England SteamWorks
  • MilanD
    MilanD Member Posts: 1,159
    edited March 2018
    2 things:

    1. Check the feed pump float switch as it may be sticking which will cause the water level to go higher and eventually flood the boiler. It may be faulty. This will lower the condensate tank level to the point where it will call for water (usually, this is where the make-up water goes on systems with the tank). Next thing you know, boiler is flooded and condensate tank is full. The only other remote possibility is that somehow the vacuum is being created at the boiler side, at the end of the cycle, and this is sucking the water up from the 0 psi side on and from the condensate return tank.

    2. High pressure may solve this by defaulting to higher op pressure and not allowing the system to drop into vacuum (or try to)... FT trap keeps psi 0 at the condensate tank side, and there should be a check valve somewhere after the pump motor and before the Hartford loop going into the equalizer. This is to keep water from backing out of the boiler, but not from vacuum sucking it into the boiler. So, raising pressure may fix this. However, just add a vacuum breaker at the boiler side somewhere, as it's better and cheaper to operate vs. to waste fuel to maintain higher op pressure.

    Plus, if it in fact the system runs on such high pressure, venting is probably inadequate and/or the boiler is most likely oversized.