Found Airtemp Furnace locked out on open pressure switch fault code. Tested pressure switch using manometer and meter. Hot surface ignitor was not glowing despite pressure switch making. OEM hot surface ignitor reading 15 ohms/ visible corrosion. Homeowner agreed to renew plan membership and replace hot surface ignitor with a universal hot surface ignitor. Replaced hot surface ignitor and tested operation. Completed gas furnace tune up. Checked all electric motors and components. Checked gas pressure. Cleaned flame sensor. Filter ok. Combustion test: Good Completed Gas Furnace Inspection Form. Gas Furnace is operating well at the time of this tune up.