I go to a customers house for a stove that keeps shutting down and eventually find that the pressure switch is bad and replace it, still the stove shuts down and although I had already brushed the liner vent I did it again. When I got to what I thought was the end of the run I pushed the rods up multiple time in case the was a block when the brushes came back down out fell parts of a liner? They seemed really thin and shredded I was at a loss. Then the customer told me the rest of the story. A few years back the chimney was extended for an addition they did. Obviously the liner no longer reached and more would have to be added which they did but instead of getting liner they just got some dryer vent hose and used that and eventually the salts ate through the vent hose and it collapsed in the chimney. We pulled the liner out through the house coupled an additional length of chimney liner and all was well again. One for the books!