The F3 error code indicates a problem with the oven temperature sensor, the electronic oven control (EOC), or the wiring in between.
To test the range someone needs to access the rear of the EOC. The 2 violet wires go from the EOC to the oven temperature sensor. At 70 degrees the resistance of the sensor should be around 1100 ohms. If the sensor checks good, the EOC is defective. If the resistance of the sensor tests out of specifications another test needs to be made directly at the sensor to eliminate the wires.
If you problem is intermittent it becomes more of a problem and is difficult to test. The intermittent error codes are usually caused by a bad connection which causes the resistance to vary.