Robot mower shows E5 and refuses to start; often after rain or washing.

Safety first: Disconnect all power and remove the battery if the manual permits. Do not operate the mower when wet.

• Dry the mower: Move the mower to a dry, ventilated area. Open the top cover and allow it to dry for at least 24 hours. Do not use a heat gun; mild warm air from a distance is acceptable.
• Inspect rain sensor: On many Parkside models, the rain sensor is a small PCB or pair of metal pads on the top housing. Check for dirt, algae, or corrosion. Clean gently with isopropyl alcohol and a soft brush.
• Check seals: Inspect the rubber gasket around the keypad and display window. Replace if cracked or missing to prevent future water ingress.
• Check wiring: Ensure the rain sensor cable is firmly connected to the main PCB and not pinched or damaged.
• Test after drying: Reassemble, reconnect the battery, and power ON. If E5 clears when dry but returns after every light rain, the sensor or its seal is likely compromised.

When to replace: Replace the rain sensor PCB or the complete top cover assembly if corrosion is severe or the sensor tracks are eaten away.