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Help! My Steam Radiators sound like buzz saws (not like a water hammer)

This is a new sound that started happening this evening. It’s very loud!  Managed to take videos of two of my radiators doing it:

Video 2: https://imgur.com/a/0bzD2mP (louder)

What on earth is causing this to happen? And more importantly does anyone know what I can do to fix it?

Here’s what I know for sure:
- the sound occurs when the boiler shuts off after delivering all the steam throughout the system.  There’s no such sound immediately after the call for heat or even while steam propagates throughout the pipes.
- the only change to the system recently was that one of the two air vent valves in the basement was leaking steam so I replaced it with a brand new one from my local plumbing supply store
- it’s not a PSI issue, my steam boiler is showing a PSI around 1

Did I just install a faulty main vent? Here’a a pic of the new vent (https://imgur.com/a/KV5ehSn), it replaced a nicer Gorton one that a plumber recently installed a couple weeks ago. But this Gorton one was releasing a ton of hot steam, not air.

Please if anyone has any ideas I’m all ears.


  • ethicalpaul
    ethicalpaul Member Posts: 5,704
    edited December 2022
    At the end of a call for heat, all the steam in the system condenses to water which creates a vacuum in your system. You are hearing the air being pushed into your system from outside it.

    What vents do you now have in your basement (these are your "main vents" btw)? If your nice gorton main vent was leaking, your guy should have replaced it with a new one.

    I don't like those little "knight helmet" vents on your convectors, you might try Maid O Mist or Gorton or some other brand that won't make such a racket. But this might be solvable in the basement with different main vents there.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • ccordero
    ccordero Member Posts: 15
    edited December 2022
    The main vent I just installed was the T-95 Legend valve which has a 1/2 x 3/4” size. I asked for a main vent valve at my local plumbing supply store and this is what they gave me.

    found the spec sheet online. Is this the wrong size?


    My basement has two main vents, I’m not sure what the other one is but it’s also metallic and looks similar to this T95 one.

    when the plumber put the Gorton valve it wasn’t releasing steam at first but now it is, which is why I replaced it. I’m wondering now if I should have just called the plumbers back.
    JUGHNE Member Posts: 11,062
    When the word "Economy" is included in the description, they are being honest.

    IIWM, I would to to Supplyhouse.com for Gorton's.
  • TonKa
    TonKa Member Posts: 104
    It sounds to me like your convectors are resonating from the vacuum pulling air back into the system. While I am only speculating, a failing shut or extremely slow main vent would significantly increase the vacuum in the mains. The convector vents would need to suck in more air and faster than the convectors would normally handle.

    Who knows if I'm right? However, since the low quality main vent you have now probably does not vent quickly (if it works at all), you should probably get a better one, anyway.

  • Waher
    Waher Member Posts: 251
    If they didn't make that noise prior to changing out the main vents, than the problem is caused by your new main vents. The sound appears to be from the convectors resonating while refilling with air after the steam cycle ends. I would change out the vent for a larger Gorton (either #1 or #2 depending on the length/size of the main) and swap out the nipple below to try to get 6" above the elbow to protect the vent from any hammering condensate that could damage it.