No heat in Duluth. Check and find gas 17 year old gas furnace lock out I safety. Test and find duct system undersize for equipment, high static pressure, poor supply and return plenum and air distribution plenum molded. Find inducer assembly locking up and high temperature. Find ignition and flame sensor worn and weak. High CO level due to incomplete combustion. Pressure switch also worn and not closing properly, intermittent loose connection. Furnace blower assembly not balance. S making noise. No drain pan or water protection. Customer need consultation visit.