LG Microwave Error Codes: F1, F3, F5, F-3, F-9 & More

Common Symptoms

• F1 code — microwave runs but heating is inconsistent or stops early
• F3 code — microwave won't start or door interlock fault
• F5 code — keypad unresponsive or certain buttons don't work
• F-3 code — microwave shuts off unexpectedly, possible overheating
• F-9 code — microwave won't start, no power relay engagement
• Completely dead — no display, no response, power light off
• Cooling fan runs constantly or doesn't run at all

Most Likely Causes

1. 1

   F1 — Thermistor Fault

   F1 means the control board is reading an abnormal resistance from the cavity thermistor (temperature sensor) — either open circuit (OL) or shorted. The thermistor EAB35923001 is a negative temperature coefficient (NTC) resistor: at room temperature it reads approximately 10kΩ, and resistance decreases as temperature rises. Test cold: unplug the microwave, locate the thermistor (small disc-shaped component mounted in the cavity or near the magnetron), disconnect the wiring harness, and probe with a multimeter in resistance mode. At room temperature (68–77°F), a working thermistor reads approximately 10kΩ. OL or near-0Ω = failed thermistor, replace with EAB35923001. F1 on a cold microwave with a working thermistor reading suggests a control board fault rather than the sensor itself.

2. 2

   F3 — Door Switch Fault

   F3 indicates one or more door interlock switches have failed. LG microwaves use a 3-switch door interlock system: primary switch, secondary switch, and monitor switch. The correct replacement order is critical — replacing the monitor switch before confirming the primary and secondary switches are functional can blow the line fuse (a secondary $5–$15 repair). Part number: EBF61315801 (verify model match). Test each switch with a multimeter: with the door actuator pressed, the switch should show continuity; released, it should show open. A switch that doesn't change state needs replacement. Also inspect the door latch cam for cracks — a broken cam prevents proper switch actuation even with new switches installed.

3. 3

   F5 — Shorted Keypad

   F5 means the control board detected a stuck key or short in the membrane keypad. LG-specific note: F5 is sometimes caused by moisture in the flex ribbon connector between the membrane and the PCB — not a failed membrane itself. Before ordering a replacement membrane (EBR73625301), remove the control panel and inspect the flex ribbon connector for moisture or corrosion. Dry thoroughly with compressed air or 90%+ isopropyl alcohol; allow to dry completely; reseat the connector firmly. If F5 persists after drying and reseating the connector, the membrane has failed — replace with EBR73625301. Note: EBR73625301 is a membrane assembly that includes the ribbon cable; if only the PCB is faulty, the board is a separate part.

4. 4

   F-3 — Thermal Cutout Tripped

   F-3 (with a dash, distinct from F3 which is the door switch code) indicates the thermal cutout has tripped. The thermal cutout EAB35923001 is a one-shot safety device that opens when the microwave overheats. Common causes on LG over-the-range models: blocked or grease-saturated vent filters above the cooktop (the microwave exhausts upward or outward through these filters — clean or replace them every 3–6 months); running the microwave with an overfilled cavity that blocks internal airflow; or a cooling fan that has seized. Test the thermal cutout with multimeter continuity mode: working = near 0Ω; failed = OL. Replace the thermal cutout, then address the root cause of overheating before resuming normal use.

5. 5

   F-9 — Power Relay Fault

   F-9 means the main control board's power relay has failed — the relay that switches the magnetron and other high-voltage components on and off. Part number: EBR78643401 (main control board — the relay is typically not serviceable separately). F-9 often appears as a startup failure: the microwave won't initiate a cook cycle even when all other components check out. Before replacing the main board, verify the door switches are functioning (F3 can sometimes display as F-9 on some firmware variants), and check the line fuse. Main board replacement is a Medium–Hard repair requiring safe capacitor discharge before accessing internal components.

6. 6

   No Display / Completely Dead — Ceramic Fuse

   A completely dead LG microwave — no display, no lights, no response — is most commonly caused by a blown ceramic fuse (EBF35812304), a 20A/250V fuse located inside the cabinet near the power line input. This is the single most common LG microwave repair. The fuse blows from power surges, door switch failures (arcing), or a one-time overload. After replacing the fuse, identify the root cause: test all three door switches for correct operation, as a failing monitor switch causes arcing that blows the fuse repeatedly. Fuse cost: $3–$8. Access: unplug the microwave, remove the outer cabinet (6–8 screws), locate the ceramic fuse in a fuse holder on the power board or chassis near the power cord entry.

7. 7

   Cooling Fan Error — Fan Motor Fault

   LG microwaves display a cooling fan error when the fan motor (EAU61603507) fails to achieve rated speed or stalls completely. The cooling fan runs during cooking and for a period after the cycle ends to cool the magnetron and electronics. A seized or slow fan causes the thermal cutout to trip (F-3) and eventually damages the magnetron. Test: unplug the microwave, spin the fan blade by hand — it should turn freely with no binding. Probe the fan motor terminals with a multimeter (continuity mode) — OL = failed motor. Replace with EAU61603507. On over-the-range models, also clean the grease filters and the fan housing — accumulated grease is a common cause of fan motor seizure.

Quick DIY Checks

1. 1Power reset: unplug the LG microwave for 30 full seconds. Restore power and test. LG microwave error codes — especially F5 and transient F1 — sometimes clear after a power reset caused by a one-time moisture or voltage event. If the code returns during the first cook cycle, proceed to component-specific diagnosis.
2. 2Enter diagnostic mode (supported models): with the microwave idle and powered, press the 0 and 1 keys simultaneously. On compatible LG models (LMV2031ST, LMHM2237BD), the display will show stored fault codes. Record all displayed codes — multiple codes can help identify whether a primary failure (e.g., blown fuse) has caused secondary faults.
3. 3For no display / completely dead: unplug the microwave and remove the outer cabinet (typically 6–8 Phillips screws on back/sides). Locate the ceramic fuse EBF35812304 — a 20A/250V fuse in a holder near the power cord entry. Test with multimeter continuity mode: a working fuse reads near 0Ω; a blown fuse reads OL. Replace with an identical 20A/250V ceramic fuse. If the replacement fuse blows immediately, a door switch (F3) or shorted component is causing the repeat failure — do not keep replacing fuses without identifying the root cause.

1. 4Test thermistor for F1: unplug the microwave. Access the cavity thermistor (mounted on the cavity wall or near the magnetron — refer to service diagram for your model). Disconnect the two-wire harness. Set multimeter to resistance mode. At room temperature, probe the two terminals — a working LG thermistor reads approximately 10kΩ. Well below 5kΩ or OL at room temp = failed thermistor, replace with EAB35923001.
2. 5For F5 (shorted keypad): before ordering a membrane, remove the control panel (typically 2–4 Phillips screws behind vent grille). Inspect the flex ribbon connector — look for moisture, condensation, or corrosion at the connector contacts. Use compressed air to dry the connector; if corroded, clean gently with 90%+ isopropyl alcohol on a cotton swab. Allow to dry fully (30 minutes minimum or until visually dry). Reseat the ribbon connector firmly. Reassemble and test. This step resolves approximately 20–30% of F5 codes without a part replacement.
3. 6Test door switches for F3: unplug the microwave. Remove the outer cabinet. Locate the three door switches (primary, secondary, monitor) near the door latch. Test each with multimeter continuity mode by pressing the actuator manually — should show continuity when pressed, open when released. Replace any switch that fails continuity test. Replace in order: primary switch first, then secondary, then monitor. After replacement, test before installing the monitor switch to verify primary and secondary are working correctly — prevents repeat fuse blowing.

Repair vs Replace

Recommended Tools & Parts

• LG Microwave Ceramic Fuse EBF35812304 (20A/250V)

  20A/250V ceramic fuse for LG microwaves. Most common LG microwave repair — fixes completely dead/no-display units. Verify amperage rating before replacing. Identify root cause (door switch) if fuse blows repeatedly.

  $3–$12

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• LG Microwave Door Switch EBF61315801

  Door interlock switch for LG microwaves. Fixes F3 door fault. Test all three switches (primary, secondary, monitor) before ordering. Replace in correct order to avoid blowing line fuse.

  $8–$22

  Buy on Amazon →

• LG Microwave Thermistor / Thermal Cutout EAB35923001

  Thermistor and thermal cutout for LG microwaves. Fixes F1 (thermistor — 10kΩ at room temp) and F-3 (thermal cutout — continuity test). Verify which component failed before ordering.

  $10–$28

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• LG Microwave Keypad Membrane EBR73625301

  Replacement membrane keypad for LG microwaves. Fixes F5 shorted key error. Check flex ribbon connector for moisture before ordering — many F5 codes resolve with connector cleaning.

  $25–$58

  Buy on Amazon →

• LG Microwave Cooling Fan Motor EAU61603507

  Cooling fan motor for LG microwaves. Fixes cooling fan error and prevents thermal cutout tripping. Spin blade by hand first — binding fan = seized motor. Check grease buildup on OTR models.

  $20–$48

  Buy on Amazon →

• Digital Multimeter

  Required for testing fuse continuity, door switch function, thermistor resistance (10kΩ), and fan motor continuity. Ohms and continuity modes used throughout LG microwave diagnosis.

  $15–$45

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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