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Boiler knocking

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Lately we have been having issues with cast iron 180 deg. Boilers knocking. We have done the basics from adding Fernox products, and flushing boiler with vinegar. Fernox has worked well except in 1, a 15-year-old cast iron slant fin. It started about a year ago. We can not get it to stop after trying Fernox and circulating vinegar only through boiler. Any suggestions?

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  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    edited January 2020
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    What do you mean by knocking? How long does the knocking last? What part of the heating cycle is the knocking most prominent? Is it a SlantFin Galaxy? What does the Tridicator say, pressure and temperature, when this is knocking? Have you isolated the knocking to some part of the system or boiler?
  • WAYNEPEINE
    WAYNEPEINE Member Posts: 4
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    Sorry knocking! entire time burner is on. 180 deg. 20# psi boiler. my guess is full of lime? we have ran Fernox f2 silencer in it 2 times, lasts for a while. Ran vinegar circulating in boiler only. Works for a while. Any other chemicals you guys suggest?