Display shows E03; freezer may not defrost properly and ice builds up on the rear wall or around drawers.

Safety first: Disconnect power before accessing the evaporator or heater. Risk of electric shock and sharp metal edges.

Diagnostic steps:

• Check for heavy frost: Remove drawers and inspect the rear interior wall. A thick, even sheet of ice indicates defrost failure.
• Access heater assembly: Remove the inner rear panel to expose the evaporator and defrost heater (usually a metal or glass-encased element at the bottom or woven through the coil).
• Test heater continuity: Disconnect heater leads and measure resistance with a multimeter. A typical Bosch defrost heater will show a finite resistance (often 50–300 Ω). If it reads open (OL), the heater is faulty.
• Check defrost thermostat / thermal fuse: Locate the defrost thermostat or thermal fuse clipped to the evaporator tubing. Test for continuity at freezing temperature. An open thermostat/fuse will prevent heater operation.
• Inspect wiring: Look for burnt connectors, melted insulation, or broken wires between the heater, thermostat, and control board.
• Replace faulty components: If the heater or thermostat is open, replace with Bosch-approved parts. Ensure all connections are tight and insulated.
• Control board: If heater circuit tests good, the main control module may not be energizing the heater. This typically requires board replacement.

After repair: Manually defrost any remaining ice with towels and a hair dryer on low. Do not chip ice with sharp tools. Restore power and monitor for normal defrosting over several days.