Freezer shows error A4; unit may not defrost properly and frost builds up on the back wall.

Safety first: Unplug the freezer before any disassembly. The defrost heater operates at mains voltage and can cause shock.

• Manual defrost first: If the evaporator is heavily iced, unplug the unit and allow it to defrost completely. This may temporarily restore cooling and confirm a defrost system issue.
• Access heater: Remove the internal rear panel to expose the evaporator and defrost heater (usually a metal or glass-encased element at the bottom or woven through the coil).
• Visual inspection: Look for burnt spots, broken heater tubing, or melted connectors. Check the defrost thermostat/thermal fuse clipped to the evaporator for signs of overheating.
• Continuity test (advanced DIY): With a multimeter, test the heater and thermal fuse/thermostat for continuity. An open reading indicates a failed component that must be replaced.
• Replace faulty parts: Order the correct Hotpoint-Ariston defrost heater and/or defrost thermostat by model number. Install the new parts, ensuring all connections are tight and insulated.
• Reassemble and test: Refit the evaporator cover, restore power, and monitor for normal frost pattern and absence of rapid ice buildup over several days.