Freezer beeps and shows E4; defrost cycles may not occur, leading to heavy ice buildup on evaporator and poor cooling.

Safety first: Unplug the freezer and allow sharp ice to soften before working near the evaporator. Do not chip ice with knives or screwdrivers.

Step-by-step checks:

• 1. Inspect for heavy frost: Remove the inner rear panel to view the evaporator. If it is completely encased in ice, the defrost system is likely at fault.
• 2. Locate defrost sensor and heater: The defrost NTC is usually clipped to the evaporator tubing; the heater is a metal or glass element at the base or woven through the coil.
• 3. Test defrost sensor: Disconnect the sensor and measure resistance at freezer temperature and again at room temperature. Lack of change or open/short readings indicate a bad sensor.
• 4. Test defrost heater: With the unit unplugged, disconnect heater leads and measure resistance. A typical heater will show a finite resistance (e.g., 50–300 Ω). An open circuit means the heater is burned out and must be replaced.
• 5. Check thermal fuse/thermostat: Many Hansa freezers include a thermal cutoff in series with the heater. Test for continuity; if open at normal temperatures, replace it.
• 6. Control board relay: If sensor and heater circuit are good, the defrost relay on the main board may not energize. Listen for relay clicks during a forced defrost (if service mode is available) or inspect the board for damage. Replace the board if the relay or driver circuit has failed.
• 7. Manual defrost: As a temporary measure, fully defrost the unit by unplugging and leaving doors open for 12–24 hours, protecting the floor from water. This will restore cooling temporarily but does not fix the underlying issue.