Wallbox charger displays 'Error 03' and refuses to charge; often described as insulation or isolation fault.

Safety first: Do not use the charger if there is any sign of water inside the unit or connector. Turn off the upstream breaker before opening the enclosure.

• Visual moisture check: Inspect the outside of the Wallbox and the cable for signs of condensation, water streaks, or corrosion. If the unit is outdoors, verify that the weatherproof cover and cable gland are intact and tight.
• Drying procedure: If you suspect moisture, disconnect power, unplug the vehicle, and allow the charger and cable to dry in a sheltered, ventilated area for at least 24 hours. Do not apply direct heat (no hair dryers or heaters) to the electronics.
• Inspect cable entry and seals: With power off, check the cable gland and rear gasket of the Wallbox for cracks or gaps. Tighten or replace the gland and gasket if they are compromised.
• Internal inspection (qualified technician): Open the Wallbox housing and look for condensation, corrosion on the PCB, or tracking marks on the insulation. Clean light corrosion with isopropyl alcohol and a soft brush; replace the main control board or wiring harness if insulation damage is visible.
• Insulation test: A professional should perform a megohmmeter test between live conductors and earth according to Wallbox specifications. If insulation resistance is below the minimum threshold, replace the affected cable or internal harness.

If Error 03 persists after drying and seal inspection, the charger should be serviced or replaced by an authorized technician.