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 HOT SURFACE IGNITER AND FOUND BURNT OFF SILICONE AND WHITING. Cleared pressure ports and tubing. Checked amp draws on blower and inducer motor. CHECKED CAPACITOR R:10 A:8.2 MFD. CHECKED COMBUSTION 12.2% OXYGEN AND 14 PPM. Static total .53" w.c. Temp rise 52 degrees REPLACED FAILING HOT SURFACE IGNITER AND 10 MFD CAPACITOR. COMBUSTION AFTER BALANCE WAS 9.0% OXGEN AND 26 PPM. TESTED FURNACE