Need help troubleshooting my Lennox G23 furnace. When on Auto it starts up, pilots ignite but as soon as it heats up getting ready to turn the blower fan on it shuts completly down, even our digital thermostat goes completly blank like the battery is dead. (which we replaced so it is new) We can get it to run by doing this: reset the thermostat or flip the power switch on the furnace, turn on the heat on auto, once it gets to the point its about to kick the blower motor on we turn the fan to "on". Troubleshooting so far has consisted of: cleaned ignitor, new thermostat battery, took the red wire and white wire on the thermostat and hooked together but still shuts off when blower gets ready to come on, checked that there was no loose wires. Please anyone have any ideas?