question for HVAC guys

My interim plan was to set the fan switch to ON and then select heat. Fan running continuously couldn't harm anything but my power meter.
A chill in the air woke me about 4:AM . Relay had dropped out anyway. I smacked the side of the unit to get run and went back to bed. I moved the fan switch back to AUTO about an hour ago and its working fine.
I wont be surprised to find there is a fan motor problem involved. It is 24 years old.