1. Inspect gas valve for corrosion, leaks, restriction of gas flow, and abnormal noise.
  2. Inspect pilot/ safety/ thermocouple/spark ignitor.          
  3. Inspect combustion chamber for sooting cracks and deformities.
  4. Service high limit control.
  5. Lubricate blower motor and bearings.
  6. Service air filtration system.
  7. Clean and service gas burners.
  8. Clean and service pilot light.
  9. Service flame baffle (or ribbon).
10. Set manifold gas pressure.
11. Service fan control.
12. Check temperature rise.
13. Set burner air adjustment for proper mix of air and gas.    
14. Check flue and venting for obstructions and carbon monoxide leaks.
15. Service wiring assembly and tighten loose connections.
16. Check thermostat heat anticipator.
17. Perform match test in heat exchanger.    
18. Check for gas leaks around connections.