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Dunham valve

I am new to this site so forgive me if I do this wrong. I have a customer with a steam system piping i have yet to come across. This radiator doesn't get hot anymore. My thought is the valve with the adjustment (thermostat) possibly. Would anyone know how to check this? or where to find this.
Any help would be terrific.
John Celentano


  • Jamie Hall
    Jamie Hall Member Posts: 22,972
    Is the trap on the outlet working? It may be failed closed. That would be more likely than that Dunham inlet valve failing. Another possibility would be something preventing the outlet from draining freely, though that's less likely.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 16,736
    Could also be an air venting problem. This is a Vapor system, so the main air vent is in the basement, probably near the boiler.

    @DanHolohan has an excellent book you should read, which covers Dunham and many other Vapor systems:

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • mattmia2
    mattmia2 Member Posts: 9,475
    That valve is not thermostatic or otherwise dynamic, it stays to the opening you turn it to. Frequently they have a stop set that limits the amount of incoming steam to the amount the emitter can condense when they are all the way open if the boiler pressure is controlled correctly.
  • bburd
    bburd Member Posts: 893
    It is also possible that a trap on a nearby radiator has failed open, allowing steam into the common return piping and preventing the cold radiator from heating. This is the curse of systems with steam traps.