The error code's F3&F4 are codes that mean their is a problem with the oven tempature sensor and that sensor is uncappable of telling the control board what the temp. is in the oven. This is what the sensor looks like,
To check the sensor,unplug it and place meter leads into the white plastic plug at the end and check for between 1060-1100 ohms of resistiance when its good.
The F3 error code means that the sensor is shorted so if it indeed is shorted the meter reading will show ZERO ohms resistiance instead of the 1060-1100 of a good one.
The F4 error code is for sensor that has a open circuit,so instead of the 1060-1100 of a good it the display on the meter will show infinate resistiance ( the meter display will not change)
If on either the F3/F4 error code if at room tempature when checking the oven sensor if the display shows anything other that 1060-1100 ohms the sensor is going to be the problem and needs to be replaced.