Performed heating maintenance tune up service on two dual fuel systems checking all electrical components, refrigerant balance, unit start up, light off, operation, and shutdown. Cleaning of furnace burners and flame sensors, flushing condensate box, trap, and treatment of condensate lines. Checking of all furnace safeties, gas pressure, performed full combustion analysis on furnaces checking Flue gas temperature, CO, CO2, and O2 in furnace flue. Everything looks and runs great!