Display shows E4 and the unit stops; often occurs when tanks are not correctly installed or when tipping the machine.

Safety first: Unplug the carpet cleaner before adjusting internal parts.

• Re-seat both tanks: Remove the clean water and dirty water (recovery) tanks. Empty, rinse, and reinstall them firmly until they click into place. Many AEG units use tank position sensors that trigger E4 if not seated.
• Check the dirty tank float: Open the dirty water tank and locate the float assembly. Ensure it moves freely up and down. Clean off lint, hair, and detergent residue that may cause sticking.
• Inspect tank presence switch: With the tank removed, locate the small lever or microswitch that detects the tank. Press it by hand and listen for a click. If it does not click or feels loose, the switch may be faulty and should be replaced.
• Check reed switch and magnet (if fitted): Some AEG models use a magnet in the float and a reed switch in the body. Ensure the magnet is still attached to the float. Test the reed switch with a multimeter while moving a magnet near it; replace if it does not change state.

Do not bypass safety switches; they prevent overflow and water damage. Replace defective switches or float assemblies with AEG-approved parts.