Manufacturer: Day and Night
Gas Furnace
Model #
394GAW036050A
It's a 1985 model...

So all was working good, then we decided to replace the original thermostat. Wrong wiring or something, now the fan is ALWAYS stuck on, even with all thermostat wires disconnected. That's with the bottom door closed. When open, the switch does work and the fan goes off.

Any ideas on the issue?

* replaced main board, still same problem
* new board, checked purple fuse - good
* checked transformer - ~27.5v AC (it's rated at 24v, so assuming good).

Is a thermosensor problem? I'm not sure where to look or test for this one.
I do see a 3 wire, maybe sensor on the bottom by the ignitor.

Any help appreciate!
Thanks
-dan