My friend bought a quad Castille insert...got about 4 tons through it lg,la Cretes,vermonts. At the end of the season it would not run on high. Finally got the tech out today and he said the reason was fines built up in the Auger causing it to turn slower, which would cause the fan to not go on high. To me this sounds like shenanigans but know for sure you folks would be able to verify or debunk this as being the cause.