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Thread: Radiator hissing noise

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  1. #1
    DIY Senior Member wallygater's Avatar
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    Default Radiator hissing noise

    Cast Iron radiators, built in to the wall, with steel covers on them. When I remove the cover they look like a block of black iron. They all have steam valves on one end. This is a steam heat system, Very old, from the 1940`s
    There is one in each room of the house, some big, some small. Great heat, very comfortable. What is making two of them hiss? What causes the hissing noise?
    wally

  2. #2
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    Steam displacing the air. It's supposed to hiss. No hiss = no heat.

  3. #3
    Jack of all trades frenchie's Avatar
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    No, it's not - it should be inaudible/quiet.

    Hissing means the valve is stuck open, usually by debris from the system, happens as they get old. They're not closing when the steam gets to the rad, letting steam escape.

    You need to replace the air valves. Those are the silver-colored disks or cones screwed into the radiator at one end. Easy job, just make sure the boiler's off when you do it.
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    No, they hiss as the air is displaced from the radiator then when the steam hits the element the element closes and it should stop then and only then.

  5. #5
    Jack of all trades frenchie's Avatar
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    If you say so...

    Me, I've never heard a vent hiss (not so you'd notice, anyways), when it was working properly. Only when they've crapped out & are letting out steam, instead of closing like they're supposed to, does it get noticeable.

    I type this, btw, sitting at a desk that's right next to a steam rad. I can reach over & touch the vent without even stretching my arm out. My desk has been in this spot through the last 5 winters. I'm on steam heat, so is just about everyone I know.
    Master Plumber Mark:

    there is nothing better than the
    manly smell of WD 40 in the air
    while banging away on brass with a chisel and hammer...

    it smells like......victory......

    do not hit your thumb...
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  6. #6
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    Frenchie, I believe peter is right on this one. You must have your steam vents on a low setting that's why you don't hear them.

    John

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