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Noisy startup but good combustion numbers (mod/con boiler)

mtrudel
mtrudel Member Posts: 6
edited December 2020 in Radiant Heating
All,

I have a Peerless PF-80 boiler installed & on its third season (Southern Ontario, so from Oct-May). This season the boiler has started vibrating / making noise at startup, with severity ranging from a quiet normal startup to being loud enough to wake me up at night across the house.

At first glance it sounds pretty obviously like bad / delayed combustion, but I've had our hydronics guy back to analyze combustion & the numbers are perfect. We also tore the HX down and it looks in great shape internally. Some notes:

* The vibration occurs with varying severity, from totally normal startup about 1/3rd of the time through to being audible across the house about 1/3rd of the time.
* The noise sounds not unlike the vibration of dragging a chair across a wooden floor. mp3 file is attached.
* The noise happens only at ignition; the boiler runs normally once lit.
* Combustion numbers are bang-on, both high fire and low fire.
* Tear-down of the HX reveals nothing out of the ordinary.
* Occurs with and without the case opened, so air availability / temperature is likely not an issue (the outdoor intake vents directly into the enclosure).
* Outside / system temperatures don't seem to affect the likelihood of the noise, nor its severity.
* Gas supply line is new & well sized (3/4" CSST).
* The delay from spark to vibration is pretty constant, so I'm not convinced it's delayed combustion either
* My hydronics guy isn't super familiar with Peerless as a brand, so we're both a bit blind to anything specific there

We are both at a loss as to the possible cause of this. If anyone has any firsthand experience with this, or ideas about what to look at next, I'm all ears.

Thanks!

Comments

  • mtrudel
    mtrudel Member Posts: 6
    edited December 2020
  • Leon82
    Leon82 Member Posts: 684
    Fog horn sound?

  • mtrudel
    mtrudel Member Posts: 6
    edited December 2020
    Nope, it's not a foghorn - it actually sounds more like the sound of a stool or chair being dragged across a floor; that same sort of shuddering vibration.

    I posted an mp3 above where you can hear the startup sequence, with the noise coming in around 13s. I recorded that about 5' away from the boiler & represents a pretty good example of the sound (though it gets much louder than that on occasion).
  • Zman
    Zman Member Posts: 6,559
    I can't open the audio file.
    Harmonics through the gas line can cause the noise you describe in modcons.
    Are you on propane or natural gas? How much gas pipe is between the regulator and the boiler? Is it CSST or black pipe?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • SuperTech
    SuperTech Member Posts: 1,638
    Post some pictures of the boiler.  I'm betting that the sound is from flexible gas line being used.  That's a typical culprit for this type of problem. 
  • mtrudel
    mtrudel Member Posts: 6
    edited December 2020
    It's about a 3' length of 3/4" CSST until the manifold, at which point it's about 25' of 1" black pipe (outdoor) to the gas company regulator on the side of the house.

    Some photos attached. I never thought to notice, but the bends in the CSST are pretty tight -- could that be the culprit here?





  • mtrudel
    mtrudel Member Posts: 6
    Apologies about the audio link - I think this should work: https://easyupload.io/j3a7b5
  • mtrudel
    mtrudel Member Posts: 6
    Video uploaded at

    @SuperTech / @Zman is that the sound you mean?
  • Zman
    Zman Member Posts: 6,559
    I have not heard that noise before.
    Clean and inspect the venturi and fan?
    Observe flame and gas pressure when the noise occurs?
    Make sure there is not a donkey with a digestive problem hiding behind the boiler? :|
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • SuperTech
    SuperTech Member Posts: 1,638
    That's different from the typical noise from CSST gas line. I must admit that I haven't heard anything like that before. Almost sounds like my impact driver. Perhaps its the solenoid on the gas valve chattering? I would check gas pressure and combustion to see if that is affected when the noise occurs
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