Professional service or your money back guarantee. Replace air filter with a new one for cleaner air and prevent major damage to the system. Inspect heat exchanger for cracks and carbon monoxide leaks to protect your health. Inspect gas connector for leaks and prevent fire. Inspect vent connector for carbon monoxide leaks and protect health. Clean furnace cabinet to eliminate spider web and dust. Inspect burner jets for clogs and prevent fire explosion. Inspect pilot, igniter, main gas valve, and fan control for proper functioning. Inspect 110 & 24volt system for proper voltage & amperage. Inspect thermostat calibration for precise and optimal performance when calling for heat. Inspect system performance for maximum comfort. Check air return and supply at registers for correct volume