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Weird noises from expansion tank

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rea5245
rea5245 Member Posts: 6
in Radiant Heating

Why does my boiler's expansion tank make these noises?: https://youtu.be/Afx-tBvFafA

I have radiant floors. The tank is 5 months old. My previous tank was making these noises a lot. The service man said the old tank was waterlogged and replaced it.

This new tank makes the noises irregularly. For a while, it was every day in the early morning. One afternoon, I heard it twice in a row, ten minutes apart.

After I set up the camera, the tank was quiet for a week (or at least I didn't notice any noises). Then it made the noise again.

Thank you.

Comments

  • bjohnhy
    bjohnhy Member Posts: 206

    Interesting

    Are you sure it is the expansion tank? What is the boiler/circulator doing at this time?

    Is that a pressure gauge at expansion tank, can you set up camera to watch pressure gauge during noise episode?

    Larry Weingarten
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 12,173
    edited March 28

    I’m pretty sure that noise is not coming from the expansion tank. That might be what we call kettling. That is water boiling when it should not be.

    I would suspect this is happening inside the gas boiler’s heat exchanger, near the surface where the flame makes the water the hottest, and there is insufficient water flow through the boiler to move that heated water away from the hot spot fast enough to keep it from boiling.

    I would like to see what the near boiler piping looks like. Can you post a photo of the boiler from farther back so we can see all the pipes and pumps under and around the boiler? Something far enough away to see like this:

    Screenshot 2026-03-28 at 1.08.54 PM.png

    Your boiler model number would be helpful too. and your actual piping may be different

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • rea5245
    rea5245 Member Posts: 6

    I was in the room once when it made the noise, so I could put my head between the tank and the boiler. The sound is definitely coming from the tank or the pipes near the tank.

    No lights change on the boiler during the noise, so I assume the boiler isn't doing anything.

    That's a good thought about watching the pressure gauge. It's somewhat visible in my video, and it's not making any big movements. But maybe there are small movements that I could set up a camera to see.

  • HomerJSmith
    HomerJSmith Member Posts: 2,778
    edited March 28

    That Ex-tank appears to me to be a #15 and not a Extrol Pro #30. Maybe too small. Get a automotive stethoscope at a auto parts store or Harbor Freight and see if you can pin point the source of the noise.

  • rea5245
    rea5245 Member Posts: 6
    https://forum.heatinghelp.com/discussion/comment/1893107#Comment_1893107

    It's an EX-30PRO.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 12,173
    https://forum.heatinghelp.com/discussion/comment/1893106#Comment_1893106

    Then it must be happening near a circulator pump. the pic of the system would help

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • rea5245
    rea5245 Member Posts: 6
    https://forum.heatinghelp.com/discussion/comment/1893109#Comment_1893109

    The circulator pump is to the right of the boiler and not visible in the video. But when my head is between the tank and the boiler, the noise is definitely coming from the left.

  • HomerJSmith
    HomerJSmith Member Posts: 2,778

    Take a pic of the connection of the Ex-tank to the sys,

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 12,173

    @rea5245 thank you for your reply.

    I’m over 90% certain that the expansion tank is not the source of that noise. There really isn’t anything inside that tank that can make that kind of sound. The only moving part is a flexible membrane that separates air from water, and it simply moves slightly as the pressure in the system changes—it doesn’t create noise like what you’re hearing.

    A more likely cause is something called cavitation in the circulator pump. This can create a rattling or rumbling noise. Cavitation happens when the pressure in the system is too low. At lower pressure, water can actually start to boil at a lower temperature than normal. So even though the water isn’t extremely hot, it can briefly turn into tiny steam bubbles inside the pump.

    As the water moves through the pump, the pressure increases again, and those bubbles quickly collapse back into water. That rapid forming and collapsing of bubbles can create the noise you’re hearing. In simple terms: the pump may be causing tiny bursts of boiling and collapsing bubbles because the pressure is too low—and that makes the noise.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • rea5245
    rea5245 Member Posts: 6
    https://forum.heatinghelp.com/discussion/comment/1893139#Comment_1893139

    If that's the case, what's the remedy?

  • Larry Weingarten
    Larry Weingarten Member Posts: 4,096

    Hi, Something is preventing pressure at the inlet of the pump from remaining at system pressure, so running the pump lowers inlet pressure. Might be the way the plumbing is configured or could be a check valve. Pictures showing more of the plumbing would be helpful. I do think @EdTheHeaterMan is onto something. 😺

    Yours, Larry

    bjohnhy
  • rea5245
    rea5245 Member Posts: 6

    Here's a picture.

    IMG_20260329_080626_1.jpg
  • Kaos
    Kaos Member Posts: 872

    The sound could be from the air separator. You could have some gunk in there that is occasionally restricting flow when it makes it to the air sep.

    EdTheHeaterManbjohnhy

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