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Air Vent on Steam Radiator Won't Stop Hissing

About two days ago (nearing the end of our heating season), the air vent on my main steam radiator started hissing without regulation, meaning it just keeps going when steam is flowing. I can't visibly "see" steam coming out, but I can feel and hear it.

I imagine this is a straightforward problem as it just started, but I couldn't find a resolution on this page. I'm not sure if it means it just needs to be replaced, but thought I would ask before testing random amateur ideas out there.

Any and all advice is greatly appreciated!


  • ColdNights
    ColdNights Member Posts: 21
    I also checked and the boiler is at proper psi with and the sight glass looks as expected
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    How many ounces is your pressure?—NBC
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,832
    My guess is the vent just failed. See if you can replace it with an identical model vent.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • neilc
    neilc Member Posts: 2,703
    and a quick picture of the boiler, gage, Ptrol, and pigtail
    is the gage after the pigtail, with the Ptrol?
    or are they separate?
    known to beat dead horses
  • ColdNights
    ColdNights Member Posts: 21
    Thanks! It is at/below 2 psi.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Is that pressure measured on the 0-30 psi gauge?
    It may not be accurate at the lower pressures needed for these systems. Best would be a 0-3 psi gauge, on a tee with the pressuretrol, and the original gauge.—NBC