Dual-zone Vestfrost wine cooler displays E4 and the lower zone temperature is unstable or not cooling.

Safety first: Disconnect mains power before working on the cooler. Use insulated tools and avoid damaging insulation.

Steps to check and fix:

• 1. Locate lower zone sensor: In most Vestfrost dual-zone units, the lower sensor is mounted on the rear wall or side wall of the lower compartment, sometimes behind a small grille.
• 2. Inspect sensor and cable: Remove any cover and check for physical damage, discoloration, or moisture. Follow the cable path to ensure it is not pinched by shelves or panels.
• 3. Test the sensor: With the unit unplugged, disconnect the sensor from the PCB and measure resistance. Compare to the expected NTC value at the current temperature. Replace if open, shorted, or significantly out of range.
• 4. Replace if needed: Gently pull out the old sensor, feed the new sensor cable through the same hole, and secure it in the original position. Avoid kinking the cable.
• 5. Check PCB connection: Clean the connector pins on the control board and ensure a snug fit.
• 6. Power up and verify: Reconnect power, clear the error by cycling power if necessary, and monitor the lower zone temperature for several hours.
• 7. If unresolved: Persistent E4 with a new sensor suggests a faulty main control PCB, which may require professional replacement.