What F4 means (lg f4 error)
An lg f4 error on an LG wall oven indicates a lower-cavity temperature sensor (RTD) fault on a double wall oven — the lower sensor reads out of range. As with the upper sensor, the control cannot regulate that cavity and faults out, so the lower oven will not heat correctly.
Symptoms to look for
The signs below help confirm you are dealing with this condition rather than a different fault on your LG Oven. You may see one of them or several together, and they can build up gradually or appear suddenly after a power event, a long door opening, or recent service.
- The display shows “F4”
- The lower oven will not heat or hold temperature
- The upper oven may still work
- Lower-oven baking was inaccurate before the code
Common causes
Several different faults can produce these symptoms. Working through the most likely causes in order helps separate a quick, owner-level check from a problem that needs trained service and the correct LG parts.
- Failed lower RTD sensor — the sensor reads out of range
- Disconnected sensor plug — the harness came loose
- Damaged sensor wire — a chafed or melted lead
- Control input fault — the measuring circuit fails
Troubleshooting steps you can try
Work through these checks in order before calling for service. Stop wherever you are unsure, or where high-voltage parts, gas, the sealed refrigeration system, or a heat-pump compressor are involved, and hand the rest to a qualified technician.
- Press Clear/Off, then switch the oven breaker off for 30-60 seconds and restore.
- Use the upper cavity if needed while the lower is diagnosed.
- Do not bake in the lower oven while F4 is active.
- If F4 persists, leave it for service to measure the lower RTD.
Parts a technician may replace
Depending on what the diagnosis shows, a technician may inspect, test, or replace the lower-cavity temperature sensor (rtd), sensor harness, and control board. The correct part for your LG Oven is matched from the model and serial number, and genuine LG components are fitted rather than generic substitutes so that performance, safety, and the appliance’s long working life are all protected. Confirming the failed part before ordering avoids replacing more than the fault actually requires.
When to call a technician
F4 needs a technician to measure the lower-cavity RTD and replace the sensor or repair the connection. When the fix calls for trained service, book a visit through our scheduling page and an experienced, qualified technician will diagnose and repair it. For manufacturer documentation and model lookup, see the manufacturer at lg.com/us.
Prevention and care
Regular care keeps this condition from returning on your LG Oven. Keep filters, vents, and the condenser or exhaust path clean, avoid overloading or blocking airflow, check that doors and seals close cleanly, and follow the LG maintenance guidance for your model. Because this unit relies on electronic control, protect it with a stable, correctly rated power supply and have any built-in or laundry installation done to LG specification so the control never sees an out-of-range condition. If a code appears, note exactly what was shown before you reset the appliance — that record helps the technician reach an accurate diagnosis and avoid replacing parts unnecessarily.
Related help and LG resources
Browse other LG Oven diagnostics, read about professional LG Oven repair, look up your unit in the LG models reference, or the related F1 upper sensor fault, or schedule a service visit. For LG manufacturer documentation and model lookup, visit the manufacturer at lg.com/us.
