F4
Ultima Cosa
Temperature Sensor Drift / Calibration Error
F4 error appears intermittently, often when the unit is hot.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Aging NTC sensor with incorrect resistance curve, Poor thermal contact between sensor and cavity, Loose sensor mounting screw, Control board calibration out of range
How to Fix / Troubleshooting
Safety first: Unplug and cool the unit before accessing the sensor.
- Check sensor mounting: Locate the cabinet temperature sensor and ensure it is firmly attached to the cavity wall or bracket, not hanging loose.
- Inspect wiring: Wiggle the sensor harness gently while monitoring continuity with a multimeter. Intermittent readings indicate a failing sensor or connector.
- Replace sensor: Install a new Ultima Cosa-compatible NTC sensor if readings are unstable or out of expected range at room temperature.
- Control board: If a new sensor does not resolve F4, the control board's calibration may be faulty and the board should be replaced.
Accurate temperature sensing is critical for safe operation; do not bypass or short the sensor.
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Repair Difficulty
Medium
3/5
Required Part
Cabinet Temperature Sensor (NTC Probe)
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