F5
LG
Oven Control Board Relay or Watchdog Failure
LG oven shows F5 and may not start or may shut off mid-cycle.
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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 oven control board (relay or logic fault), Power surge damage to PCB, Loose control board connectors
How to Fix / Troubleshooting
Safety first: Disconnect power at the breaker before opening the control panel.
- Power cycle: Turn the breaker OFF for 5–10 minutes, then back ON. If F5 reappears immediately, suspect the control board.
- Access control board: Remove the rear panel behind the control console. Locate the main oven control board (ERC/PCB).
- Inspect visually: Look for burnt spots, cracked solder joints, or swollen capacitors. Check that all wire harnesses are fully seated and not loose.
- Check incoming power: With power ON (only if you are trained and equipped), verify correct voltage at the board input using a multimeter. Incorrect supply can cause watchdog errors. If unsure, skip this step and contact a technician.
- Replace control board: If no wiring issues are found and F5 persists, replace the oven control board with an LG-approved part. Transfer any mounting hardware and reconnect all harnesses exactly as original.
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Repair Difficulty
Professional Required
5/5
Required Part
Oven Control Board (ERC/PCB)
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