LG Oven F3: The Temperature Sensor Circuit Is Broken

F3 means the ERC board cannot get a valid resistance reading from the oven temperature sensor (RTD probe). The circuit is either open (infinite resistance — wire broken or sensor burned out) or shorted (near-zero resistance — wires touching). Without temperature feedback, the board refuses to energize any heating element.

F3 Means No Baking at All

With F3 active, the oven will not heat. The board requires continuous temperature monitoring to safely control the heating elements — without it, there is no way to prevent overheating. This is a hard lockout. The cooktop/rangetop functions (gas burners or electric surface elements) are typically unaffected because they have their own independent temperature controls.

Testing the RTD Sensor

The RTD (Resistance Temperature Detector) is a platinum wire probe mounted inside the oven cavity at the upper rear wall. It extends about 4-6 inches into the cavity. Its 2-wire connector exits through the rear wall to the ERC board.

At the Sensor

1. Turn off the 240V breaker
2. Disconnect the sensor connector (accessible from the rear of the oven or inside the control console area)
3. Measure resistance across the two sensor pins:
   • At room temperature (68 degrees F): expect 1,080-1,100 ohms
   • Infinite (OL) = open circuit. The platinum wire inside the probe has burned through or a lead wire has broken
   • Near zero (under 100 ohms) = shorted. The two lead wires are touching inside the probe or in the connector
   • Within range = sensor is fine. Check the harness next

At the Board

1. Disconnect the sensor harness at the ERC board end (2-pin connector)
2. Measure resistance at the board connector (from the sensor, through the harness, to these pins)
3. If the reading differs significantly from the reading taken directly at the sensor, the harness has a break or short

Wire Harness Failure

The sensor harness runs from the oven cavity through the insulation and frame to the ERC board. This path exposes the wires to heat (especially near the oven cavity exit point) and vibration. Common failure points:

• The grommet where wires exit the oven cavity — heat degrades insulation here first
• Where the harness passes near the oven vent — hot exhaust air accelerates insulation breakdown
• The connector at the board end — heat and age corrode the pins

Inspect the entire harness path. A wire with cracked or missing insulation can short to the oven frame, creating an intermittent F3 that appears during heat (when the metal expands and makes contact) but clears when cold.

Sensor Replacement

1. Breaker off
2. Inside the oven: remove the 1-2 screws holding the sensor bracket to the upper rear wall. Note the sensor's probe length extending into the cavity
3. Push the sensor probe out toward the rear. The wire follows through the wall
4. At the rear: disconnect the old sensor connector
5. Connect the new sensor (MEG52785806 or model-specific, $15-30). Route the wire through the rear wall hole
6. Inside: push the probe into the cavity and secure with screws. The probe tip should extend about 4 inches into the cavity
7. Restore power. Run a bake test at 350 degrees F. Verify the oven heats and F3 does not return

Parts and Cost

F3 During Self-Clean

The self-clean cycle's extreme heat (850-900 degrees F) can be the final stress that kills an aging sensor or harness. The platinum wire in the RTD probe has expanded and contracted thousands of times over the oven's life. A wire that is fatigued but intact at 400 degrees F may finally break at 900 degrees F. F3 appearing during or immediately after self-clean is a common presentation.

F3 vs. F2: Same Sensor, Different Failures

F3 means the sensor circuit is broken — no reading at all (open or shorted). F2 means the sensor works but reports an excessively high temperature. Both involve the RTD probe, but F3 is a circuit integrity failure while F2 is a temperature value failure. The diagnostic approach starts the same (test resistance at the sensor) but the conclusions differ.

Using the Cooktop With F3

Gas burners on LG ranges operate independently from the oven's ERC board. If F3 locks out the oven, the gas burners still function normally via their own ignition system. Electric surface elements may or may not be affected depending on whether they share the ERC board — check your model's wiring diagram.

---

LG oven dead with F3? The RTD sensor is a $15-30 part — we test in place and replace same-visit. Book sensor repair.