Klarstein portable AC stops and displays E4; sometimes accompanied by water tank full indicator.

Safety: Turn the unit off and unplug it before draining water.

Steps to resolve:

• Drain the tank: Move the unit to a location where water spillage is acceptable. Remove the lower drain cap or connect a short hose to the drain outlet and drain all water into a container.
• Check float switch: On many Klarstein portables, a float or water level switch is inside the lower pan. Remove the rear panel and verify the float moves freely and is not stuck by dirt or scale. Clean with warm water and mild detergent.
• Inspect drain hose: If a continuous drain hose is installed, check for kinks, clogs, or elevation above the unit that could prevent drainage. Ensure the hose slopes downward continuously.
• Level the unit: Use a spirit level to ensure the unit is on a flat, level surface so water flows correctly to the tank or drain outlet.
• Sensor check: If the float switch uses a small micro-switch or magnetic reed sensor, inspect the wiring and connector to the PCB. Replace the float switch or water level sensor assembly if it is mechanically damaged or electrically open.

If E4 returns immediately after draining and cleaning, the water level detection circuit on the main PCB may be faulty and require professional service.