I have a Carrier Infinity System that is just over a year old. It has the Infinity Control. There is no installed humidifier. About once a week I'll notice the blower running when the the interiro temp. is well within the set points. The fan will not turn off if I set System OFF, and it will not change speeds when I adjust the fan speed (normally on Auto). If I power sequence the furnace, everything remains normal for about another week. It is like the control and system board stop talking. Is this a fail-safe mode of some kind?