The fan on my Honeywell Chronotherm I've fan keeps running constantly even after the system is shut off - no heat, no cool. How do I turn it off? Thanks!

Turn off the power to the furnace. Then find the defective part and replace it. It is possible a relay in the furnace went bad or the thermostat internal relay welded together. Good hunting.

Thanks for your help. We'll work on it this weekend. Hope this will take care of the problem!