Trane XE78 furnace comes on fine then goes out.

[mrdb]

Hello my Trane XE78 comes on fine, heats up and blows warm air. After after some time the fire goes out but the blower keeps on running, and running. I turn off the switch at the thrmostat, wait a few minutes and turn it back on. It comes on and runs fine again.
Model number is TUD140C960A0

Found the flame sensor, took it out and cleaned it gently with light sand paper.
The flame sensor looked fine. Clean when I took it out.
The furnace is 11 years old.

Problem persists. After observing the furnace for some time,

1. Furnace starts up fine.
2. Runs fine, heating for over a minute.
3. Reaches some internal temperature, then shuts the flame off, keeping the large forced air blower running circulating heat.
4. Soon, the internally temperature falls needing more heat. I can see the igniter light up. I see the igniter light three times and go out, but the flames never start. Guess, no gas is released?
5. During all this time the red light is flashing steadily, about once per second. After the third time the igniter comes on, but fails to light the red light starts flashing twice.


thanks.

[V]

[Jake Jones]

Hello mrdb! was the problem in your gas valve?. Just checking since I had the same problem and replaced my own with new valve at approx. $68 bucks. Just wondering.