Display shows E4 and the unit may not defrost properly; heavy ice buildup on evaporator or frequent temperature swings.

Warning: Disconnect the appliance from mains before servicing. Allow any ice to melt to avoid water near live parts when power is restored.

E4 often indicates a problem with the defrost sensing or heating circuit in De Dietrich wine coolers that use automatic defrost.

• Access evaporator area: Remove the internal rear panel to expose the evaporator, defrost heater, and associated wiring.
• Check for ice: If the evaporator is encased in ice, allow it to fully defrost with the unit unplugged. Place towels to catch meltwater.
• Inspect defrost sensor: Locate the defrost NTC (often clipped near the heater or on the evaporator). Check for broken wires or corrosion. Test resistance at room temperature and again in ice water; resistance should increase significantly in cold.
• Test defrost heater: With wires disconnected, measure heater resistance. A typical small heater will read between 50–300 Ω. If open (OL), the heater or thermal fuse is blown.
• Check thermal fuse (if fitted): Some De Dietrich models include a thermal cut-out in series with the heater. Test for continuity; replace if open.
• Board relay check: If sensor and heater test good, the defrost relay on the main PCB may be faulty. Visual signs include burn marks or a melted relay case; replacement of the control board is usually required.
• Reassemble and monitor: After replacing faulty components, reassemble, restore power, and monitor for normal defrost cycles and absence of rapid ice buildup.