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Munchkin T40M rumbles and vibrates when firing from low temp

First time poster here, homeowner. CA, Bay Area.

Had the T40M Munchkin Boiler installed about 10 years ago to support radiant heating. It seems to definitely be struggling lately to hold temps when the temp drops outside to <40.

Recently, it has started rumbling and vibrating when it fires up at low temps.

The two use cases are:
1. Temperature on the boiler is around 70-90 in the early afternoon when the outside temperature is warmer. When the boiler fires up at this temperature late at night, it starts rumbling each time the boiler fires. And this goes on every minute or so, and can sometimes go for over an hour. When the temp reaches about 120, further firing does not seem to make the unit rumble. The sound is like a large truck stalling.

2. It seems to especially also happen when the temperature dips to <40. Not often in CA, but it still does. When the temp is around 40 +, the system does not seem to rumble.

The tech from the company who installed it came out and could not reproduce it because he comes in the morning when the temps are at 125 or 128. Turning unit on/off etc does not reproduce it.

Can this be fixed? Or is it time to replace the munchkin? I also reached out to HTP with this issue.

Help!

Comments

  • fenkel
    fenkel Member Posts: 135
    Have you checked the fan assemble? Its made up with plastic and can wear out and wobble on start ups.
    Any codes?
  • Zman
    Zman Member Posts: 6,559
    When is the last time it was disassembled and cleaned? Has a combustion analysis been performed recently?
    Munchies are great little boilers, they need regular serving.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    HomerJSmith
  • SuperTech
    SuperTech Member Posts: 1,638
    Zman said:
    When is the last time it was disassembled and cleaned? Has a combustion analysis been performed recently? Munchies are great little boilers, they need regular serving.
    This was my first thought as well.  These boilers are very maintenance sensitive.  They need to be properly cleaned and tuned annually. Combustion analysis is essential for providing reliable operation.
  • kcopp
    kcopp Member Posts: 3,715
    The swirl plate inside may need to be replaced.
    Zman
  • HomerJSmith
    HomerJSmith Member Posts: 1,292
    edited December 2020
    Did HTP make a T40M? What is the nameplate model #.

    It's a combustion issue as Zman suggests. Clean it and do a combustion analysis on it with a recently calibrated CO meter.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 2,781
    edited December 2020
    The rumbling sounds as though the gas/air mix is too rich and needs to be adjusted by someone that has a manometer.
    I'm in Berkeley if you want to talk about it. (510)773-9870 cell

    Munchkin boiler sizes are T50M, T80M, T140M and T199M.
    Often wrong, never in doubt.
  • HomerJSmith
    HomerJSmith Member Posts: 1,292
    I dug out an old manual and all I see is a T50M and a T80M.
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