Performed furnace maintenance on 2008 Lennox heater 1. Found that flame sensor has oxidization occurring and could lead to failure of blower start up in heating mode 2. Evaporator coil contain no secondary float switch in case of coil overflowing and water damage 3. Blower wheel assembly is very dirty and covered and debris 4. Found cracked washer on heat exchanger, washer is used for stabilization when She change it expands and contracts this needs to be watched closely and examined every year for cracks