I have a Superior Fireplace "Heatform" fireplace that was installed in 1984.  The "Heatilator" type airflow through tubes around the firebox worked well up until a year or so ago.  Since then the airflow through the system has decreased to almost nothing.  With the two fans on a very small amount of air does come through.  It appears that something has plugged the system but I cannot see,  not that there is much of the system visible, any obstruction.  Any ideas as to what has happened to the air flow system?
	
		
			
		
		
	
				
			 
	 
	 
 
		 
 
		