Hi All. I am experiencing once again a phenomena I experienced last season that I call 'kettling' which I believe is caused by the water near the fire tubes flashing and causes the so called kettling sound in the boiler and the heating zone copper piping to pulse. I tried a number of things last season to eliminate the sounds based upon suggestions from others on the forum. Ultimately my thought was that I was using wood that was too dry as I had a batch of kiln dried hardwood I was burning. I started burning some higher MC fuel and the sounds stopped. Well a year later the sounds are happening again and I am using wood with a MC of around 15% per my meter. I have posted a you tube video of the sounds and was wondering if anyone had any further input especially you guys with the Tarm gassifiers. I actually heard a couple of rumbles earlier that really made my heart race. When I shut the draft fan off the kettling stops. The you tube link is below. Any help much appreciated. The original post I believe is archived under 'Boiler Kettling' as well.