I have a Waterfurnace Premier2 closed loop system since 1996. Last year I had a fan motor failure which was replaced. Since then twice an airflow fault has occurred. In both instances resetting caused it to go away. I have not noticed any performance issues. From what I have read the airflow fault is caused by motor RPM being sensed low and there is no actual airflow sensor. My question is there a way to isolate the problem as we go south for the winter and turn the heat down but not off. When the airflow fault occurs the waterfurnace shuts down. Thanks for any insight.