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Vaporstat gets stuck


My steam heating system stopped working suddenly and upon further investigation I noticed that the flask with mercury in the Vaporstat Honeywell gets stuck in tilted position which prevents the system from working. When I touch or tap on the Vaporstat the flask tilts back and the systems starts working again. Please see the picture.

Any ideas on how to fix this? Do I have to replace the Vaporstat and if so which one should I get which is more reliable?
Thank you!


  • Chris_L
    Chris_L Member Posts: 336
    Looks like you've got a Pressuretrol, not a Vaposatat.

    If the switch is not coming back on after the boiler pressure returns to atmospheric, it is likely because the "main" - the "differential" is less than zero. Try reducing the differential. If that doesn't work, then also increase the main, but just a bit (2 psi should be good.)

    The scales aren't very accurate, so you really can't put much faith in their numbers.
    EBEBRATT-Ed Member Posts: 15,544
    1st step is to remove the control and make sure the pigtail and the pipe connections into the boiler are clear of sludge. Also check the bottom of the control.

    I just noticed that is not a vapor stat it is a regular pressure control
  • Jamie Hall
    Jamie Hall Member Posts: 23,324
    And one other thing not mentioned above. The mercury type -- which is far more reliable than the modern microswitch type, by the way; don't lose it! -- is very sensitive to being level. Place a known high quality level across the top of the case and adjust the pigtail so it is exactly level.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,062
    Those usually have a hanging pendulum in the inside back on the right side.
    There is a white dot of paint below for that to be lined up on.

    As Chris L said, maybe a little more difference between settings also.
  • Gordo
    Gordo Member Posts: 857
    edited December 2021
    In my not so humble opinion, Honeywell's L404A-1354 was their worst pressure control commonly encountered.
    It is no longer made and good riddance.
    I would remove it, dispose of the Hg properly (hazardous waste), and install a PA404A pressuretrol instead.
    At least that is more or less adjustable to get it to work in the proper ranges.
    I would also remove that steel pigtail and replace it with a brass pigtail.
    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.