Furnace Maintenance: Checked operation of thermostat. Changed filter and also cleaned grille. Checked for gas and co leaks. Checked amp,draws on blower motor and inducer motor. Cleaned furnace housing, blower and burner compartments. Pulled and polished flame sensor. Cleared pressure ports and tubing. Cleared condensate drain line. Combustion check 7.6% oxygen and 24 ppm. Static total .51" w.c. Installed Lennox Germicidal UV bulb!