Performed air duct cleaning and sanitation on a 5 bedroom single system house. All vents and ductwork are clear of dust and debris at this time. System is functioning properly at this time. Recommend duct cleaning every 3-4 years. I did notice an abundance of rust in the ductwork above the unit due to running the humidifier too high. Performed a preventative maintenance on the heater. Customer said the thermostat was turning blank after running for a little while. After inspection I noticed when the thermostat went blank the high limit code on the furnace was coming up. System will need a coil cleaning to prevent that from happening. Also their was a leak on the exhaust vent that will need a little bit of silicone. Other then that system is running good. Cleaned the flame sensor, also cleared out the trap for the furnace drain. Amped out the The blower motor and the inducer motor. Condensate pump is working. System is operating at this time.