F-1 Serious Moderate DIY

LG Microwave F-1 — Oven sensor open / thermistor fault

LG Microwave · Error code F-1

What F-1 Means

The oven temperature sensor (thermistor) circuit is open. The control board can't read cavity temperature, so sensor-based cook cycles (Auto Cook, Sensor Reheat, Popcorn) won't run correctly.

Symptoms

  • F-1 or F1 on display
  • Sensor Cook / Auto Cook cycles fail immediately
  • Microwave still runs in manual time-cook mode
  • Unit beeps and stops mid-cycle

Common Causes

1
Failed thermistor

The sensor probe (typically 10K-ohm NTC) has opened. Most common cause.

2
Disconnected sensor harness

Plug at the thermistor or at the control board has vibrated loose.

3
Pinched / broken sensor wire

Wire damaged where it routes past the cavity vent.

4
Main control board fault

Sensor input circuit on the PCB has failed — replace only after ruling out the probe.

How to Fix It

  1. Unplug the microwave for at least 60 seconds, then restart — clears transient faults.
  2. If over-the-range, remove from mounting plate or pull from countertop and remove the top/back grille for access.
  3. Locate the oven thermistor (small probe in the cavity wall or top duct) and unplug its connector.
  4. Measure resistance across the thermistor leads with a multimeter at room temperature — should read roughly 10K ohms. Open (OL) means the sensor is bad.
  5. Inspect the harness from sensor to control board for chafe, pinch, or melted insulation.
  6. Replace the thermistor if out of range or open; reconnect firmly.
  7. If sensor reads correct and harness is good, replace the main control (PCB) board.
  8. Reassemble, restore power, and run a Sensor Reheat test cycle to confirm.

Parts You May Need

If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.

Common replacement LG microwave thermistor / oven sensor View on Amazon→ Common replacement LG microwave main control board View on Amazon→

More LG Microwave Codes

CH CH / Child Lock — Control locked DOOR DOOR / Door Error — Door switch / interlock fault EE EE — EEPROM / control memory error F-2 F-2 — Keypad / touch panel shorted F-3 F-3 — Key short / specific button stuck F-4 F-4 — Humidity / steam sensor fault

All LG codes → All microwave codes →

Verified against manufacturer documentation: lg.com

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician.