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No Steam at 2-pipe radiators in 1920's School Building 3rd Floor

Chuck_20 Member Posts: 13
We have a 1920's school building with pipes in the walls feeding wall ventilators and radiation. No prints.
It's a two pipe system. I'm looking for some possibilities to look for in diagnosing the problem of no steam at the control valves. The third floor of the building has three radiators against the wall fed vertically by separate lines. One of the radiators works the other two do not. The two that do not have steam are cold up and down stream of the control valve at the radiator. We have not been able to trace any of the lines as of yet.

1. My first thought is that the traps may not be passing air to allow the steam to rise through the pipe.
Question: If air is not being released is it possible to still have cold pipes at the radiator? Will some steam rise up the vertical pipes?
2. I also read that cracking union to see if air is released and steam starts flowing would be a good indication that the traps need repair or replacement.
2. A valve could also be shut on the riser in the basement. We'll need to trace the risers in a large building.

Any confirmation or help in heading me in the right direction would be appreciated.


  • Fred
    Fred Member Posts: 8,542
    Have you checked the dry returns that those radiators drop into? Is there a vent on that return, in the basement? Are they on the same return as the one that works? Are these radiators at the end of the main in the basement? Is the radiator that works supplied by the same main that feeds the two that don't work? It is possible that the traps have failed closed. Pictures of the radiators, piping and pertinent components of the system, in the basement would help others determine the type of system it is and help them provide you with some clues.
  • nicholas bonham-carter
    A trap failed shut could explain no steam in the inlet pipe, as steam would not rise up such a small pipe.You could make the boiler fire by setting up the thermostat, and either crack the union nut on the trap, or the top cover. This would allow air to escape and steam to arrive. As you probably know, the insides of most traps can have a new cage installed. Saillah, one of our members makes the innards for them, so do a search for his name, and contact info here. Changing a trap unnecessarily is a terrible chore with removing the old spud, whereas changing the cage is relatively easy.
    There is another possibility: that some crossover traps have failed, thus preventing the final escape of the air; however in that case I would expect a larger group of failed radiators in the same area.—NBC
  • Jamie Hall
    Jamie Hall Member Posts: 23,655
    Your first thought is probably correct, as the others have noted -- bad traps. Easy to fix, easy to diagnose (but a caution: if you are going to open the top of the trap as suggested, or crack the union open, have someone in the basement to shut off the boiler right now if steam comes out. That stuff hurts when it hits your hand...).

    However, if is also possible that your thought of a valve -- or valves -- in the basement might be closed. Older systems sometimes have valves in unexpected locations, and that is worth checking on in any event.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,109
    Everything NBC said. Also when was the last time they did heat?
    I have an old school from that vintage. There has been a lot of hacking on the system.
    Someone new in the building may have noticed some rads not heating and perhaps they never have heated recently.
    The risers in the basement could have been cut off and capped etc.

    To have 1 out of 3 working would be the standard norm in my 1919 school as massive windows have been replaced with much smaller.
    Walls have been insulated etc. Some were capped in the basement, but rads left in place connected, some were capped at the floor and rad tossed out.
  • Sailah
    Sailah Member Posts: 826
    You can buzz the cover off a trap and inspect it. Most traps fail open but some do fail closed. I'd personally test with cover off vs breaking the union nut but it all depends how easy it is for the covers to come off. I use an 18V 1/2" impact gun with the correct socket. If you don't have that type of tool it may be safer to crack the union nut, I just find they leak afterwards. If opening up a way for air to vent solves the problem then you either have a bad trap bellows or plugged return.
    Peter Owens