Display shows E4 and the unit shuts down after a short run time.

Safety first: Disconnect from mains and allow the machine to cool for at least 30 minutes before inspection.

• Clean air paths: Remove the dirty water tank and inspect the air intake grill and motor protection filter. Wash or replace the filter if heavily soiled.
• Check for obstructions: Ensure no plastic bags, carpet fibers, or debris are blocking the cooling vents around the motor housing.
• Inspect thermal cut-out: Many Kärcher motors have a thermal protector wired in series. Check for loose connections or discoloration. If the protector is open even when cool, it must be replaced (often supplied with the motor).
• Verify duty cycle: Some models are not rated for continuous heavy-duty use. Confirm you are not exceeding the recommended operating time without breaks.
• Control PCB sensor: If airflow is good and the motor/thermal protector test OK, the temperature sensing circuit on the main control PCB may be faulty and require replacement.