LG Oven F4 Error — Temperature Sensor Open Fix Guide

What Does This Error Mean?

F4 means the temperature sensor (RTD probe) circuit is open — the wire between the sensor and the controller is broken or disconnected.
The oven can't heat without an accurate temperature reading.
Power-cycle once.
If F4 persists, the sensor needs replacement.
This is service-tech work — 150–250 USD typical.

Affected Models

LG LRE series electric range
LG LSE series slide-in
LG wall oven
LG ProBake convection range

Common Causes

RTD sensor probe failed (broken thermistor)
Sensor wire disconnected from controller
Wire damaged where it routes through the cabinet
Connector loose at the controller
Controller sensor input damaged

How to Fix It

Power-cycle the oven.

Switch the breaker off for 10 minutes.
Switch back on.
Some F4 events are transient — fresh boot can clear them.
Try a low temperature bake (250°F).
If F4 returns immediately, it's a real fault.
Check for visible damage near the sensor.

Look inside the oven at the back wall.
You should see a small probe sticking out — usually about an inch long.
That's the temperature sensor.
Any visible damage, melted insulation, or grease coating?
Note for the technician.
Don't try to access the sensor wire.

The sensor wire routes through the back wall and into the control compartment.
Replacing it requires removing the back panel and possibly the cooktop.
Service-tech work — DIY risks damaging the seal or other wiring.
Cancel any active cycle.

If F4 appeared mid-cook, food may be partially cooked.
Press Cancel to stop heating.
Open the door once cool (don't let trapped heat continue cooking).
Move food to another oven or finish on the cooktop.
Schedule LG service.

Provide model and serial numbers.
Sensor replacement is the typical fix — 1–2 hours of labor plus a 30–80 USD part.
Total bill 150–250 USD out of warranty.
Free under warranty.
Heating is impossible without this sensor — repair is needed before normal use.

Frequently Asked Questions

Can I cook with F4 showing?

No — the oven won't heat at all with F4 active.
Without the temperature sensor reading, the controller can't safely power the heating elements.
That's the safety doing its job.
You'll need the cooktop or another oven until F4 is repaired.

What's the difference between F4 and F3?

F3 is sensor short — the wire is shorted to ground or another conductor.
F4 is sensor open — the wire is broken or disconnected.
Both indicate the temperature sensor circuit isn't reading correctly, just different fault types.
Replacement is the same regardless of which code.