|If your oven fan is stuck on Check the Following
First you will need to access the fan wiring. To do this you will probally need to remove the back panel. This usually give you access to the fan assembly. Remove the wire connector. Next you can check to see if the motor is getting power, to do this connect voltmeter to wire connecter to fan. The fan should not have voltage when oven is off. If you do check the thermostat and main control.
Some ovens have a thermostat mounted usually to the top of the oven. This thermostat is usually round metal and wired to the fan. This thermostat detects heat from the oven. When a certain amount of heat is detected it allows power to travel through it to run the fan. This thermostat should have continuity when the oven reaches a certain temperature if it always has continuity replace the thermostat.
The main control may have failed. If the fan motor and thermostat check good the control is at fault and need to be replaced.