How to Fix LG Oven F9 Error Code

Fred's Appliance
July 7, 2021
Oven Repair

If you were planning to cook dinner in your LG oven but your LG oven is displaying an F9 error code, you will probably need to make alternative dinner plans. An F9 error code on an LG oven means that the oven has failed to exceed 150 degrees Fahrenheit after five minutes of preheating. There are a number of causes and solutions to the issue, which will depend on whether you have an electric or gas oven.

Reset the Oven

Sometimes, the F9 error code is the result of an electrical fault that has magnetized the circuitry. Resetting the oven by disconnecting the power for five minutes will demagnetize the circuitry and resolve the F9 error.

Relay Board

A faulty relay board is the most common cause of the F9 error. The relay control board responds to signals from the microprocessor display control board in the control panel by opening and closing relays to control voltage going to the burners, elements, or oven. If the oven is turning on but not heating sufficiently and flashing an F9 error, you will need to test the relay board with a multimeter to determine if it needs to be replaced.

If you have an electric oven, the relay board is usually located behind the range at the bottom right of the oven. If you have a gas oven, the relay board is usually located behind the range, at the top right. You will need to pull the oven out to access and remove the rear panel.

Follow these steps to access and replace the relay board:

  1. Disconnect the oven from the power source. If you have a gas oven, turn the gas off as well.
  2. Remove the screws holding the rear access panel brackets in place; then carefully remove the brackets.
  3. Remove the screws holding the panel in place and lift the panel to remove it.
  4. Disconnect the wiring harness from the relay board. Before removing, snap a picture to remember how to reconnect it.
  5. Remove the screws holding the board in place.
  6. Release the retaining clips to detach the relay board.
  7. Test the relay board with a multimeter.
  8. Remove and replace a faulty relay board.


Another of the more common reasons for the F9 error is a faulty thermostat. The thermostat is a switch that opens and closes depending on the temperature it senses. The thermostat is often damaged when the oven overheats after a cleaning cycle. It is often easy to tell that the thermostat needs to be replaced because it will have melted with the high heat. The thermostat causing the F9 error is usually located at the back of the oven.

If the thermostat has melted, then it is also likely that the thermal fuse is defective. The thermal fuse can be tested with a multimeter or visually checked for damage to see if it needs to be replaced.

To access and replace the thermostat:

  1. Disconnect the oven from the power source, and turn off the gas if you have a gas oven.
  2. Remove the rear access panel. Depending on your model, there may be up to three panels to remove to access the thermostat.
  3. Remove the two wires attached to the thermostat.
  4. Detach the metal tab holding the part in place.
  5. Remove the thermostat and replace it with a new one.


A common cause of the F9 error with an LG gas oven is that the igniter is defective. The igniter draws an electrical current to heat and ignite the gas in the burner assembly. If the igniter is defective, it will struggle or fail to ignite the gas and heat the oven. If you can see the igniter, you can check if the igniter is defective by looking at the igniter when the oven is on. If it glows red for over 90 seconds without igniting the burner or it fails to glow, it will need to be replaced. The location of the igniter may vary depending on the model.

To replace the igniter:

  1. Disconnect the oven from the power source and turn off the gas.
  2. Remove the oven door by lifting the hinge stops.
  3. Remove the shelving from the oven.
  4. Remove the screws that secure the oven’s bottom panel.
  5. Lift out the bottom panel.
  6. Remove the screws holding the burner shield in place.
  7. Remove the burner shield.
  8. Locate the igniter and remove the igniter mounting screws.
  9. Locate the wire connector and pull it up through the hole at the base. If you cannot access the wire connector, remove the bottom drawer to reach it.
  10. Disconnect the wire connector and remove the igniter.
  11. The igniter can be tested with a multimeter; however, it is often easy to tell from a visual inspection that it needs to be replaced.
  12. Install a new igniter by working backward through the above steps.

Less Common Causes

Temperature Sensor or Bulb

With electric ovens, the temperature sensor or bulb regulates the temperature in the oven. If the temperature sensor or temperature sensing bulb is defective, it can cause the oven not to heat completely and trigger the F9 error code. On most models, the temperature sensor is a probe located inside the oven at the rear.

Printed Circuit Board (PCB)

The PCB controls most of the electrical components in an electric oven, such as the thermostats and elements. If the PCB is faulty, it may be causing the oven to not sufficiently heat. The PCB is difficult to test with a multimeter but can be examined for signs of damage, such as burning or loose wires.

Faulty Gas Valve

If your gas LG oven is failing to heat, it may be caused by an issue with the gas valve. The gas valve can be examined for damage and tested with a multimeter to determine if it needs to be replaced.

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