F5
LG Control Board Relay or Power Circuit Failure

Microwave shows F5 and will not run; may occur after a power surge or during cooking.

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Failed relay on main PCB, Burned trace or component on control board, Power surge damage, Shorted load component causing board fault

How to Fix / Troubleshooting

Safety warning: Unplug the microwave immediately. Do not attempt to operate it further.

User-level steps:

  • Check outlet and power: Plug another appliance into the same outlet to confirm proper voltage. Avoid using extension cords or power strips with the microwave.
  • Power reset: Leave the unit unplugged for at least 15 minutes, then reconnect. If F5 reappears immediately, internal control circuitry is likely damaged.
  • Inspect for burning smell: If you notice any burning odor or visible scorch marks around the control panel, do not use the microwave. Keep it unplugged.

Next steps: F5 typically indicates a failed main PCB or related power relay. Replacement requires cabinet removal, high-voltage safety procedures, and post-repair leakage testing. Contact an authorized LG service center for diagnosis and board replacement.

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Repair Difficulty

Professional Required 5/5

Required Part

Main PCB (Control Board)
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