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Error code reference

LG Oven Error Code F-1

Upper oven thermistor remains open for over 1 minute after cook starts.

LG codesLG oven codes

Upper oven thermistor remains open for over 1 minute after cook starts.

First step from the service manual

Check the thermistor using test mode 4.Diagnosis; verify sensor value is 70°F–90°F at room temperature. If not, power off and measure thermistor resistance at CN04 pin 3,4 — normal is approximately 1.09 kΩ.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What F-1 means on a LG oven

The F-1 error code on an LG oven indicates that the upper oven thermistor has remained in an open-circuit state for more than one minute after a cook cycle begins. The thermistor is a temperature-sensitive resistor embedded near the oven cavity that continuously reports temperature data to the control board. When the circuit is open, no valid signal reaches the board, and the oven cannot regulate heat safely, so it shuts down the cook cycle and triggers this fault.

The thermistor connects to the control board through connector CN04, specifically at pins 3 and 4. At normal room temperature (approximately 70 to 90 degrees Fahrenheit), the thermistor should read roughly 1.09 kΩ of resistance. A reading significantly higher than this or a completely open circuit reading on a multimeter confirms the thermistor itself has failed. If resistance reads correctly at the connector but the error persists, the wiring harness between CN04 and the sensor is the likely culprit.

Common causes include a thermistor that has burned out or physically broken, damaged wiring in the harness leading to the sensor, corroded or loose connector pins at CN04, or in less frequent cases, a control board that cannot correctly interpret an otherwise functional sensor signal. Diagnosis begins with test mode 4 on the board, which displays a live sensor value. If the displayed value falls outside the 70 to 90 degree Fahrenheit range at room temperature, the next step is powering off the unit and measuring resistance directly at CN04 pins 3 and 4.

Source: manufacturer service documentation.

Common causes of F-1

  1. 01

    Failed upper oven thermistor

    Part replacement

    The thermistor element itself has broken or burned out, creating an open circuit. Measuring resistance at CN04 pins 3 and 4 will show a reading well above or completely outside the normal 1.09 kΩ value at room temperature.

  2. 02

    Damaged wiring harness

    Part replacement

    The wires running from the thermistor to connector CN04 can crack, fray, or burn due to heat exposure inside the oven cavity. Visually inspect the harness for breaks or heat damage, and check for continuity along the wire run.

  3. 03

    Loose or corroded connector at CN04

    Wiring / connection

    The connector at CN04 pins 3 and 4 may have worked loose or developed corrosion, interrupting the signal even if the thermistor itself is functional. Disconnect and reseat the connector, then inspect the pins for oxidation or damage.

  4. 04

    Broken connector pin or terminal

    Part replacement

    An individual pin inside the CN04 connector can bend, retract, or break, causing an intermittent or permanent open circuit. Careful inspection of the pin terminals with the connector unplugged can confirm this.

  5. 05

    Faulty control board

    Part replacement

    If the thermistor resistance measures correctly at 1.09 kΩ and the harness and connector show no faults, the control board may be failing to read the sensor signal properly. This is the least common cause and should only be considered after all other components are ruled out.

See the test procedure for each cause

Frequently asked questions about F-1

What does F-1 mean on a LG oven?
F-1 means the upper oven thermistor has been detected in an open-circuit condition for more than one minute after a cook cycle starts. The thermistor is the sensor that monitors oven cavity temperature and reports it to the control board. Because the board cannot verify safe operating temperatures without that signal, it halts the cook cycle and displays this fault code. The issue is located at connector CN04 pins 3 and 4 in the wiring circuit.
Can I fix the F-1 error on my LG oven myself?
A knowledgeable DIYer can diagnose this fault by using the oven's built-in test mode 4 to check the sensor reading, then measuring thermistor resistance at CN04 pins 3 and 4 with a multimeter after powering the unit off. If the thermistor reads outside 1.09 kΩ at room temperature, replacing the sensor is a straightforward repair. Wiring harness or connector issues also fall within DIY range, but control board replacement is more involved and may be better handled by a technician.
Is it safe to use my LG oven while the F-1 code is showing?
No, you should not attempt to use the oven while F-1 is active. The control board cannot monitor oven temperature without a functioning thermistor signal, which means it cannot prevent overheating. The oven will typically refuse to run a cook cycle in this condition, and operating it in a fault state could pose a safety risk.
Will resetting my LG oven clear the F-1 error?
A power reset by unplugging the oven or cycling the breaker may temporarily clear the code, but if the underlying cause is a failed thermistor, damaged wiring, or a loose connector, the F-1 error will return once you attempt to start a cook cycle and the one-minute open-circuit threshold is reached again. The fault must be repaired, not just reset.
How much does it cost to fix an F-1 error on an LG oven?
If only the thermistor needs replacement, parts typically range from around 20 to 60 dollars depending on the specific model, making it one of the more affordable repairs. If a wiring harness is damaged, parts and labor can range from 80 to 200 dollars. Control board replacement, if required, is more expensive, often falling between 150 and 400 dollars or more including labor. Getting a diagnosis completed first will help narrow down which component is actually at fault before committing to a repair cost.

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