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Apartment Building Steam Heating Problem

I have an apartment building with (1) low pressure atmospheric steam boiler. The steam pressure is set for 3 psig. The system is a two pipe system with a boiler feed unit. The boiler is rated for 780 MBH input and 624 MBH output. The building is three stories. There is only one thermostat that controls the boiler. All the radiators have manual steam supply valves and air vents. There is no visible traps on the radiators. There is also no vacuum breakers on the system.

The problem I am having is I cannot maintain steam pressure. The steam pressure starts to build and within less than 30 seconds the pressure drops like a rock and all the water is sucked out of the boiler. A few minutes later all the water comes back down the condensate lines and into the boiler feed. By this time, the boiler feed has already made up fresh water to the system and the boiler feed eventually begins to overflow.

Could this be a case where my boiler is undersized for the load and the steam is condensing too fast thereby creating a vacuum and sucking all the water out of my boiler?

Does anybody have a solution?



  • RodRod Posts: 2,067
    Pictures will be a big help.

    Hi- Could you please post some pictures of your boiler and the connecting piping so we can see what you have. Take the pictures of the boiler from different angles and back from the boiler so we can see the piping connected to it. This allows us to trace out the piping as to where it leads.  We can blow up the pictures if we need to see detail. Also pictures of one of the radiators and any other odd devices connected to the piping is a big help.

    - Rod
  • Long Beach EdLong Beach Ed Member Posts: 686
    What changed?

    Did it ever work right?  When did it stop working?

    Your problem's not vacuum, and I doubt the boiler's too small.   It might be poor water quality.  When's the last time the water was cleaned?
  • nicholas bonham-carternicholas bonham-carter Member Posts: 6,540
    water hiding

    as the pressure rises in the boiler, water will be forced up in the returns to a level which is 16 times 1.75 inches times 3 pounds = higher than i can reach. if there is a horizontal pipe in this range of height, it will hide enough water to activate the lwco, so look for that piping, drop the pressure, and report back.--nbc
  • Tim_HodgsonTim_Hodgson Member Posts: 59
    I agree with Ed

    Vacuum does not suck water out of a boiler. Carry-over does. Cleaning the inside of the boiler and then filling with clean water is a good first step.

    I think I am missing something, if your two pipe radiators do not have traps, what stops the steam from venting out the boiler feed tank?

    Good luck,

  • furnacefigher15furnacefigher15 Member Posts: 502
    2 pipe with air vents on rads?

    May be an old direct return gravity setup.

    All the radiators returns would run independently to the return main that is below the water line creating a water seal, and preventing steam flow into the return side of the system. Air vents would be needed in that set up.

    Non of that matters now though. Now that there is a condensate return pump or boiler feeder, you need steam traps for every radiator and the ends of the mains will need float and thermostatic trap's.

    You'll also need to eliminate the steam vents on the rads.

    Pictures would be helpful though. Radiators and boiler
  • SteamheadSteamhead Member Posts: 11,379
    Two other options

    1- install a False Water Line;

    2- get rid of the pump and tank, and use gravity return like the Dead men did.
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • daveycrockettdaveycrockett Member Posts: 6
    Pictures will be a big help - Reply

    I don't have any pictures currently but all the near boiler piping was piped per the drawing from Burnham.
  • daveycrockettdaveycrockett Member Posts: 6
    Piping diagram

    See attached diagram.
  • daveycrockettdaveycrockett Member Posts: 6
    What Changed - Reply

    Nothing changed to my knowledge. The boiler was a direct replacement for the one that was in there. It was replaced becasue a section was cracked. I don't think that they manage their water quality that well.
  • Dave in QCADave in QCA Member Posts: 1,660
    More Information Needed

    We really need some pictures of the near piping that connects to the system and to the boiler. 

    Also, is there by any chance a zone valve on the steam supply?  Is the boiler piped with a proper equalizer and a proper Hartford loop?

    If everything is piped right, the vacuum that occurs at the end of the steam cycle should not suck the water out of the boiler.  Something is wrong.
    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.
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