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I have a 3 year old Navien ncb240 that recently puts out a kettling(banging) sound when domestic hot water is being used,I had a plumber come to address the issue and he said the boiler was installed incorrectly. he said I lacked a looped manifold and magnetic filter. He also said my 2 gal expansion tank was too small.I flushed out the system(heat exchaner) but the noise is still present. The plumber wants thousands of dollars to do the proper work and said the kettling may or may not stop . What next?


  • hot_rod
    hot_rod Member Posts: 20,827
    While it is possible that it is mi-sized or mis-piped, if it was noise free for 3 years? something has changed.

    Same with the expansion tank, if the pressure does not exceed 25 psi when heated ups, the tank must be accepting the expansion volume?

    Does it use a plate heat exchanger inside for DHW? If so, sometimes you need to use an appropriate cleaner and flush both A and B side. Tankless cleaner kits with and acid based cleaner work for the domestic side.

    For the boiler side a product like Rhomar or Fernox, hydronic cleaners would be best.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Big Ed_4
    Big Ed_4 Member Posts: 2,541
    Thousand$ of a repair and it may work ? :) Your on the right track ,look for someone that wants to fix your system .. Banging you say, I would look for something loose in the hot water flow . First back flush the hot water side of the system .. A pebble in the water stream can cause this problem .
    I have enough experience to know , that I dont know it all