My Trane furnace, model # XE80, is about 8 yrs old. When it tries to kick on, all 3 orifices ignite, but then after about 3-5 seconds, before the blower even starts, the flames go out. Then the electric starter heats up again, and tries again. After the 3rd attempt, when the flames go out, the blower comes on only and blows cold air. This happens about 30% of the time. I must note that if I turn off/on the thermostat manually during the problem, it has always worked fine. Any and all suggestions would be greatly welcome.