This furnace is about 4 years old. Fan runs no heat, red light flashes 2 times (external lockout)...what does this mean? I know that it means that the system has tried to ignite three times and failed. I tried powering off the system and repowering, but that didn't work. It seems to ingnite and then shut off after a few seconds. It also seems that if it gets to the point where the fan is continuosly running and I do this (power off and then on) it will fire up and work for a while. I don't know if this is coincidence or if it is pertenent (just an observation) but I have tried this three times always with the same result throughout the night.