Won't run. Furnace fan and thermostat seem OK. As far as I can see, all lines are intact and clear.

Simple reset? No. Look at the the control board for a flash code. Check the fuse on the control board. How did you check" Furnace fan and thermostat"?

Thanks for answering. Where do I find the control board? As to checking, the furnace fan is running when I turn the thermostat and lower the temp below current. I would think that indicates both of those are functional. Am I wrong?

Control board is in the air handler (furnace fan) compartment. You may be able to see the codes, if any, through a front peephole.