Oven displays F4, may shut down or heat erratically, sometimes accompanied by rapid temperature swings

Safety first: Turn off power at the breaker and allow the oven to cool completely before inspection.

• Visual inspection: Remove the rear panel of the range to access the sensor wiring. Look for melted or charred insulation where the harness passes near the oven liner.
• Test sensor resistance: Disconnect the sensor and measure resistance at room temperature. A very low reading (near 0 Ω) indicates a shorted sensor. Replace with the correct La Cornue sensor.
• Check for shorts to ground: With the sensor disconnected, test each sensor lead to chassis ground with a multimeter. Any continuity indicates a harness short; repair or replace the harness.
• Dry connectors: If there are signs of moisture or condensation in the connector, dry thoroughly and apply a small amount of dielectric grease to protect contacts.
• Control board check: If sensor and wiring are confirmed good, the EOC sensor input may be shorted internally. Replace the EOC if F4 persists.