Completed furnace, maintenance and inspection. I cleaned flame sensor. I checked air pressure and temp splits. I tested components and draws. The airflow pressure on the system is well over the max. This will cause the blower to run faster than it should and has already caused heat strain on the heat exchanger. Air filter needs changed out as well as the humidifier pad. When I turned system back on during the maintenance, the gas valve quit working. We replaced gas valve and activated club membership. Furnace is operating departure.