Furnace Problem
 

My furnace not always start up when the thermostat indicates so, it
rarely happens (1-2 times a week). I wake up freezing in the middle of
the night, thermostat says system on (electronic thermostat) but system
is off or only fan is working. "Reboot" furnace and starts fine. HVAC
guys came and found no roblems anywhere, thermostat signal gets to
furnace and this one started normally every time he tested it
unfortunately and he isskeptical to replace parts with no solid
evidence of what it could be.

Any ideas?