Ice buildup on rear wall, poor cooling, E04 error shown

Safety first: Unplug the refrigerator before accessing the evaporator area. Do not use sharp tools to remove ice.

Immediate action:

• Manual defrost: Remove food to a cooler. Leave doors open and unplug the unit for 12–24 hours to melt ice. Place towels to catch water. This may temporarily restore cooling.

Further checks (for experienced DIYers):

• Access evaporator: Remove freezer drawers/shelves and the rear interior panel to expose the evaporator coil, defrost heater, and sensor.
• Inspect components: Look for broken heater elements, burnt spots, or disconnected wires. Check the defrost sensor clipped to the evaporator for secure mounting and intact wiring.
• Test heater: With a multimeter, measure resistance across the heater terminals (typically 20–150 Ω). An open circuit indicates a failed heater.
• Test defrost sensor: At room temperature, measure resistance and compare to Bosch NTC specs. Out-of-range or open/shorted sensors must be replaced.
• Check thermal fuse/thermostat: If present in series with the heater, verify continuity. An open safety device must be replaced with the exact rated part.

Note: If all components test good, the control board may not be initiating defrost cycles and should be diagnosed by a technician.