My Frigidaire gas furnace has 3 burners that ignite for a couple of seconds then shuts off. The electric ignition and fan works fine, it's just the burners that turns off after a few seconds. If I try turning the furnace on and off a few times it sometimes fires up and stays on. I have tried cleaning the flame sensor and it seems to be working now.

I cleaned the flame sensor and it seems to be working now, we will see if it remains working in the long run.