I re-read your postings again and you said there were no codes on the control board so probably not in lock out mode. A reset or recycle of power switch in the furnace should fix the lockout assuming control board is good and no codes exist. From the schematic it looks like the coach 12VDC source does connect directly to the furnace power switch and is then sent to the thermostat via blue wires from the furnace. So when not functioning I would try carefully shorting (jumping) the blue thermostat wires at the furnace to see if the fan motor starts running as is normal startup for the furnace. Intermittant wiring issues are always a PIA to track down because when working there is no probem to trace; so you have to wait until it fails again in order to troubleshoot. A multimeter and the manual schematic will help you trace where your 12vdc is failing to connect to. You also said tapping in a certain place or device area caused things to start working again....can you re create that scenario? Good luck.
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