The furnace has a controller board with these model numbers on it: "1012-940-M" "HK42Fz016". I have replaced the batteries in the thermostat (which is brand new).

The fan stays running. I turned off the system, removed the thermostat, made sure the wires are isolated from each other, and turned the system back on. After a few seconds, I hear a click, a RED LED on the controller board flashes on and off and the fan starts running and never stops.

Is this caused by a bad replaceable part on the controller board?

Thanks for your help.

Return the thermostat to where you bought it... if its new its under warranty... there are no user servicible parts on it other than the batteries.

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Originally Posted by smoothy

Return the thermostat to where you bought it... if its new its under warranty... there are no user servicible parts on it other than the batteries.

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Well, if the brand new T. stat is the cause of the problem,
then I do not understand why the fan behaves the same
way (i.e runs non stop), even after
1. turn off the system.
2. disconnect the thermostat.
3. turn on the system

So, it seems that the T stat is not in the equation.