E4 appears on the display and the compressor does not start or stops shortly after starting.

Safety first: Unplug the freezer. The defrost circuit operates at mains voltage; avoid contact with live parts.

• 1. Access evaporator and defrost components: Remove baskets and the inner rear panel to expose the evaporator coil and defrost heater assembly.
• 2. Locate defrost sensor and heater: The defrost NTC is usually clipped to the evaporator tubing. The heater is a metal or glass tube or wire element at the bottom or around the evaporator.
• 3. Check for visible damage: Look for burnt spots on the heater, broken wires, or a cracked sensor body. Replace any obviously damaged parts.
• 4. Test defrost heater: Disconnect heater leads and measure resistance with a multimeter. A typical heater reads tens to a few hundred ohms. Infinite resistance indicates an open heater that must be replaced.
• 5. Test defrost sensor: Measure resistance of the defrost NTC at room temperature and when cooled with ice. It should change smoothly. Open or shorted readings indicate failure.
• 6. Inspect thermal fuse/thermostat (if fitted): Some Severin models include a thermal fuse or bimetal thermostat in series with the heater. Test for continuity; replace if open.
• 7. Replace faulty components: Install Severin-compatible defrost sensor, heater, or thermal fuse as needed. Secure them in the original positions and ensure good contact with the evaporator where required.
• 8. Reassemble and test: Refit the inner panel, restore power, and monitor if E4 clears and the unit cycles normally without excessive frost buildup.

If all defrost components test good, the main control board may not be driving the defrost circuit correctly and should be evaluated or replaced by a technician.