​Gas (or Oil) Connections - Check all gas (or oil) connections for gas leaks.

Burner Combustion - Check burner combustion

Heat Exchanger - Check heat exchanger for cracks and hot spots.

Safety Controls - Check all controls of the heating system to better proper and safe operation.

Electrical Components - Test the voltage and amperage draw of electrical components. Check for loosen connections. 

Fan Motor - Test, clean, and oil the indoor blower motor. Check if wheels are clean. 

Air Filters – Check and replace the air filters (clean reusable filters).

Fan Belts - Test the fan belts. Check for old or loose dry belts.

Electrical - Check the electrical wiring and tighten connections if necessary.

Drain Lines - Inspect the condensate drain lines for correct performance.

Indoor Coil - Inspect the indoor coil.

Capacitors - Test the capacitors.