I have a Carrier 58STA090-16 furnace that doesn't stay on. I have a power switch next to the furnace and I can turn it off, then turn it back on and the furnace will start and run for a while (like 8 hours), then it goes stops running until I go down and reset the power switch again.

Any ideas?

Take the cover off the burner compartment of the furnace.

Observe the sequence of events that occurs at the furnace when you turn up the thermostat and post that sequence of events in order and in detail.

You should see a flashing light through a small glass window on the bottom door of the unit when it faults out. Count the blinks. You will have blinks then a short pause with blinks again Then a long pause and the code starts again. The code for the blinks are on back of the blower door.