Report "I have a Trane XB80, 8 years old. All was well for a week and it just happened again! The thermostat goes blank, does not show any numerals. I touch the black switch in the lower part of the furnace and the furnace kicks on, gas flows, thermostat shows the temperature. House is well heated. Worked well for a week and then same thing happened overnight. What is the cause? What should I do to fix this? Thank you"