Furnace Diagnostic: Upon Arrival found unit trying to start up but nothing turning on burners. Found failed hot surface igniter and a very dirty unit that was in need of service/maintenance. Replaced hot surface igniter and everything kicked on normally. Furnace Maintenance: Checked operation of thermostat. Changed 1(20x30x1) return air filter and cleaned grille. Checked for gas and co leaks. Cleaned furnace housing, blower and burner compartments. Pulled and polished flame sensor. Checked capacitor mfd ratings 7.5 Checked amp draws on inducer motor and found inducer motor over amping and on last leg Checked combustion 7.9% oxygen and 23 ppm Static .75" w.c. Found return is undersized and needs to be dealt with in future Informed homeowner that unit is definitely on last leg considering the age of equipment. Average Life is 15-20 years and his equipment is 30 years old. Also informed he needs a CO detector!