Performed preventative maintenance on a standard gas furnace. Inspected all the electrical components. Confirmed proper high and low voltages. Replaced the standard 16x25x1 air filter. Cleaned the burners, flame sensor and burner compartment. Tested the amp draw for the blower and inducer. Both are operating within the manufacturer specifications. Performed a combustion analysis on the heater. System is operating at 82% efficiency and has a CO level of 27ppm. System is operating properly at this time. Model #2A7A3036A1000AA Serial #7504L7E3F