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Kettling sounds in indirect heater

Joe_28 Member Posts: 15
edited October 2020 in Radiant Heating
I installed a system for my daughter and son-in-law's new house with a Munchkin 140M boiler and an SSU45 indirect approximately 17 years ago. In the past week, it started making "kettling" noises in the middle of the night. The sound seems to be coming from the indirect. The domestic water is from a well and treated with a softener. I've been checking it out the last couple days and cannot get it to make the noise while I'm there. Anybody have any ideas what could be causing this?


  • kcopp
    kcopp Member Posts: 3,996
    Minerals and sediment in the water settling out in the tank.
    When its heated it pops as the coil gets hot.
    Drain down the tank 100% and see what you get. May need to pull off the boiler drain... there are a couple tricks to flush out any sediment.
  • Zman
    Zman Member Posts: 7,355
    @Larry Weingarten will by chiming in soon. :)
    It may also be a hard coating has formed on the outside of the coil that expands and contracts when the coil heats up.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,584
    Hi, @Zman is correct... just can't keep away! It's strange for an indirect to be making this sound. Normally it's made by fuel burning units that have a big temperature difference between water and heat source and a layer of sediment in between, to slow down heat transfer. At fifty psi, water boils at 298 degrees F. Where in an indirect are you going to get that hot?

    Still, I'd drain and flush the tank to see what comes from it. Softening removes "hardness" but replaces it with salt, which might not be good for the stainless tank, so I'd soften as little as possible, leaving as much as 120 ppm of calcium and magnesium hardness in the water.

    Sound travels through pipe and water much faster than it does through air, making it difficult to know just where the noise is coming from. So it might be good to keep trying to get it to make the sound while you're there and can turn various things on and off to see what the effect is. Any chance it's pump cavitation? Even funner would be to capture the sound and post it here so we all can enjoy it! :p

    Yours, Larry
  • HomerJSmith
    HomerJSmith Member Posts: 1,620
    edited October 2020
    I had a situation where I had a HTP SSU45, a new installation, that had a rattling noise. A kettling sound is different than a ratting sound, but close.

    What happened in my case that was deduced by the Tech and me was that the heat exchanger coil was touching another coil loop and rattling when the indirect pump turned on. The tank was replaced.

    I assume that the indirect pump is the recommended one for your tank and boiler by HTP.

    This not the olden days, I always fill a boiler with conditioned water even it the boiler supply is connected to the street main. Water comes in all kinds of flavors and you would have to prove to me that the street water was suitable by testing it before I would use it.
  • Joe_28
    Joe_28 Member Posts: 15

    Update on the kettling sounds. Son-in-law shut off domestic cold water to tank and blew off several gallons with no visible signs of contamination. There were no noticable noises last night and today. If we have any more problems, I'm going to do as kcopp suggested. Attached is a picture of the system to give you an idea of how it's piped. Thanks for all the replies.
  • HomerJSmith
    HomerJSmith Member Posts: 1,620
    That sys sure is pertty!