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Heating Noise from Boiler, Hot Spot???

Hi, I bought a 10 year old house a year ago, and have had htis problem since day one. We get a knocking type sound from the boiler when it fires up. Not always at the same time, sometimes worse when its been off for a while, but not always. Sounds like a deep knociking sound, not like something really bad, just like a knock inside the boiler.

I am 100% positive it is inside the boiler, not a zone or a pipe. I have done a lot and contacted Utica and they were very nice, and said it is probably a hot spot, and I could try to crank up the pressure, and go to 50 psi if I change out my pressure valve. Instead i just cranked up to about 20 psi, which thye said was ok, it maybe helped a little bit with the volume of the noise.

I have had maybe 3 burner and boiler tech out, they aren;t too interested, and the problem is it not always reproduceable.

And to make it worse, you can't hear it at the boiler due to the noise of he burner firing, but if you kill the burner when it is happening, you will hear it for a few seconds, so this is how I determined it is from within the boiler, it is very clear to hear.

The reason is a problem is that it is very noticeable from the room above the boiler and took me weeks to track down the location since I couldn't figure out where it was from.

Any help you could offer or advice is apreciated.


  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542

    in the process of making cast itron, casting sand its used to create the mold. When the casting has cooled, the casting is mechanically agitated (shaken, not stirred) and the casting sand is "supposed" to fall out of the inside of the casting. Key word here is supposed. Occasionally some sand gets left behind and acts as an insulator to the transfer of heat. This causes localized boiling and steam flash. You're hearing the results of steam flash. As the manufacturer said, raising the operating pressure will supress the steam bubbles and will lessen the noise.

    I've seen this in just about every cast iron boiler manufacturer I've ever seen, including the Euros.

    One guaranteed way around it to to not use a cast iron boiler. Think Munchkin...



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  • sootmonkey
    sootmonkey Member Posts: 158

    turn your aquastat down
  • Unknown
    I'm surprised that excess make-up water wasn't mentioned

    If leaks are allowed to leak for a long time, or if you "change your boiler water", you bring in new minerals with the replacement water, Leaks and new water are usually what ends the life of a cast iron boiler.

    Steel, copper, and aluminum are affected the same way.

  • Unknown
    Water quality plays a part as well.

    New water introduced into the system will bring new minerals with it which will be deposited on the boiler surfaces and give those symptoms, also. This can happen in copper, steel, and aluminum boilers, too.

    Don't allow leaks to go unrepaired. Don't change your boiler water for no reason. This is the key to a long boiler life.

This discussion has been closed.