LG Microwave F-1 Error: Open thermistor (temperature sensor failure)
LG microwave error — here’s what you need to know. The F-1 error code on your LG microwave indicates an open thermistor (temperature sensor circuit failure). This is a Medium severity issue. What Does F-1 Mean on an LG Microwave? The F-1 error code means the microwave’s control board has detected an open circuit in […]
~30%
DIY Fixable
From $85
Typical Repair Cost
1–2 hours
Pro Repair Time
Quick Assessment
Answer to continue safely
Is it safe to keep using?
No. The microwave will not complete a cooking cycle while F-1 is active. Attempting repeated restarts will not resolve the fault and may stress other components. Avoid use until the thermistor circuit is inspected.
Can I reset the code?
Yes. A 60-second power-off reset can clear a transient F-1 error caused by a temporary sensor glitch. If the code returns immediately after reset, the thermistor or wiring requires physical inspection.
When to stop immediately?
Stop if you notice: The error returns immediately after every reset attempt, You notice a burning smell or scorch marks near the sensor area.
Symptoms You May Notice
Microwave stops mid-cycle and will not restart
The unit powers off during or at the start of a cooking cycle and displays F-1, refusing to run again until the error is addressed.
F-1 code appears on the display
The alphanumeric display shows 'F-1' immediately after attempting to start or while the unit is idle.
No heating despite fan and turntable running
In some cases the fan motor and turntable operate normally but the magnetron does not energise because the control board is blocking power due to the sensor fault.
Inconsistent temperature performance
The microwave runs too hot, too cold, or cycles erratically because the control board receives inaccurate temperature readings from the faulty sensor.
Possible Causes
Failed or open-circuit thermistor
The thermistor itself has developed an open circuit — its resistance is out of the expected range — preventing the control board from reading a valid temperature.
Requires ProfessionalLoose or corroded wiring harness connector
The connector linking the thermistor to the control board has worked loose or the pins have corroded, interrupting the signal.
Requires ProfessionalFaulty control board
The main PCB has failed and can no longer correctly interpret thermistor readings, triggering a false open-circuit fault.
Requires ProfessionalSafe Checks You Can Do
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1
Hard reset the microwave
Unplug the microwave from the wall outlet, wait 60 seconds, then plug it back in. Attempt a short cook cycle to see if the error clears.
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2
Inspect the door seal and cavity for moisture
Wipe down the inside of the cavity with a dry cloth. Excess steam or condensation near the sensor housing can temporarily trigger the code.
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3
Check the power outlet
Plug the microwave into a different outlet or test with another appliance to rule out a low-voltage supply issue that could affect sensor readings.
When to Call a Professional
Contact a qualified technician if:
- Thermistor resistance is outside the 10 kΩ–50 kΩ range at room temperature when tested with a multimeter
- Visible damage, burning, or corrosion on the wiring harness near the sensor
- Error persists after thermistor replacement, suggesting control board failure
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