Door latch switch
Common interlock fault part on appliance no-start errors.
LG microwaves (especially the NeoChef and ThinQ models) are high-tech appliances that rely on precise electronic monitoring. When your microwave beeps and shows an “F” code, it’s usually because it’s detected a problem with the keypad, the door sensors, or the internal cooling system.
Most LG microwave errors are software-based or caused by moisture and can be fixed with a simple power reset.
What This Error Means
LG microwaves use “F” (Failure) codes to indicate specific component issues.
- F-3: This is the most common LG microwave error. It means the control board detects a “Keypad Short” (a button is stuck).
- F-4: Humidity sensor error. The sensor that measures steam during “Auto Cook” is faulty.
- F-19: Heating failure. The microwave didn’t detect a temperature rise in the food.
- F-11: Inverter communication error.
Common LG Microwave Error Codes
| Code | Meaning | Severity | Fix |
|---|---|---|---|
| F-3 | Keypad stuck / Membrane error | Low | Power Reset / Clean |
| F-4 | Humidity sensor error | Low | Power Cycle |
| F-19 | No heat detected | Moderate | Check magnetron / Reset |
| F-14 | Voltage error | Moderate | Check outlet / Surge protector |
| Child Lock | Not an error! | Low | Hold “STOP” for 3 seconds |
If the display says the door is open or shows a door message before cooking starts, use the dedicated LG microwave door error guide before replacing control parts.
Step-by-Step Fix
1. Resolving the “F-3” Keypad Error
Like Samsung microwaves, LG over-the-range models can get “Keypad Short” errors from steam rising from the stove below.
- The 10-Minute Reset: Unplug the microwave for 10 minutes. This resets the control board and allows any moisture behind the touch panel to dry.
- Clean the Keypad: Use a dry cloth to wipe away any grease or moisture from the touch panel.
- The Tape Trick: If the error persists, the ribbon cable inside the door may have a tiny bit of corrosion. If you are comfortable taking the door panel off, cleaning the end of the ribbon cable with rubbing alcohol often fixes F-3 permanently.
2. Fixing “F-19” (Heating Failure)
If your microwave runs but the food is cold:
- Test with Water: Put a glass of water inside and run for 1 minute.
- Power Reset: Unplug the microwave for 5 minutes. Sometimes the “Relay” on the board that turns on the heating element gets stuck.
- If it still won’t heat: The internal magnetron or a high-voltage diode has likely failed.
3. Clearing “F-4” (Sensor Error)
- This error happens during “Auto Cook” cycles.
- The Fix: Turn the microwave off and back on. Stop using the “Sensor Cook” features and use manual time entry. If the microwave works in manual mode, the humidity sensor is the only part that is broken.
4. Disabling “Child Lock”
- If the microwave won’t respond to any buttons and shows a “Lock” or “L” icon:
- Hold the STOP/CLEAR button for 3 seconds.
- You will hear a beep and the lock icon will disappear.
Parts You May Need
- LG Microwave Grease Filter Replacement
- LG Microwave Glass Turntable Tray
- Replacement Microwave Light Bulb (LED)
- Microwave Waveguide Cover (Universal)
When to Call a Professional
Safety Warning: Microwaves can store a lethal electrical charge in their high-voltage capacitor even when unplugged. Never open the main casing of a microwave unless you are a trained technician.
- Loud Grinding or Humming: This indicates a failing magnetron or high-voltage transformer.
- Sparking inside: Usually caused by a hole in the “waveguide cover” (the silver/brown square on the side wall). You can buy a replacement cover for $5 and snap it in.
- Dead display: If the microwave has no power at all, an internal fuse may have blown.