The dip tube in stage 3 being out would be expected to mean more hot material passing up to stage 2, so stage 2 might be hotter rather than colder. However, the tipping valve ex stage 2 to stage 3 being somewhat restricted points to stage 2 being blocked and maybe full of material.

Thanks Dr. Clark

 

Indeed, the only physical problem we found was hard buildup, I suspected the buildup but I was concerned with loss of efficiency in the tower, which was not the case.