Why does the heater fan run when the heater is not in use, ie when I have it turned off.?

I just had a Honeywell Pro Th3000 Series installed. The heater has been running pretty well, but today, the heater fan kept running nonstop for about four hours. There is no off switch. It's "auto" or "on" for the fan and cool, off, or heat for the unit. It is safe for the fan to run... show more I just had a Honeywell Pro Th3000 Series installed. The heater has been running pretty well, but today, the heater fan kept running nonstop for about four hours. There is no off switch. It's "auto" or "on" for the fan and cool, off, or heat for the unit. It is safe for the fan to run nonstop?
There is really no one to call today - being new years. Please respond. I really appreciate your help.
Update: Thank you for your quick responses! I really appreciate your help!
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