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Dunkirk VLT Heat Exchanger Rumbling

JoeMagrino Member Posts: 1
We had a Dunkirk VLT boiler with indirect water heater installed about 6 years ago. This morning we woke up to some rumbling in the basement. The boiler runs fine during domestic heating in low power, but as soon as central heating kicks in, the rumbling starts while in ignition power and high power. High power only lasts for about 10 seconds before powering down and recycling again and again. There are no failure errors on the screen. I tested the CH pump in low power, ignition power and high power. The only thing I can think of is scale. Is there anything else that can be wrong? Any other troubleshooting I can do? Thanks!


  • hot_rod
    hot_rod Member Posts: 14,753
    Yes, scaled HX surfaces can create that type of noise. It is usually a gradual build up and noise. Good news is that it is fairly easy to add a cleaner, flush and add good quality water. Efficiency should bump up also. Make sure the circulator is running during any boiler call.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    HVACNUT Member Posts: 3,906
    Shouldn't a domestic call set the boiler to high fire?
    When was the last maintenance done? Is there a copy of the combustion report? 
    Just because there's no error code and it hasn't gone into lockout doesn't mean there's proper combustion. 
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