Heater function not working; water remains cold and E5 appears when attempting heated cleaning mode.

Safety first: Unplug the unit and allow it to cool completely before working on the heater assembly.

• Verify mode and supply: Confirm that you have selected a heated mode and that the unit has been running long enough for heating. Some AEG models require a few minutes to reach temperature.
• Access the heater block: Remove the rear or side panel to locate the in-line heater (metal block in the solution line). Inspect for signs of overheating or discoloration.
• Test the heating element: Disconnect the heater terminals and measure resistance with a multimeter. An open circuit indicates a failed element that must be replaced.
• Check thermal fuse and thermostats: Many heater blocks include a one-shot thermal fuse and/or resettable thermostats. Test continuity; if the thermal fuse is open, replace it and investigate causes of overheating (blocked flow, limescale).
• Inspect NTC sensor: If fitted, test the temperature sensor (NTC) resistance at room temperature and compare with AEG specs. A shorted or open NTC will trigger E5.
• Check heater relay on PCB: Look for a heater relay on the main control board. If the relay contacts are burnt or the relay coil is open, the heater will not energize. Replace the relay or the entire PCB as per AEG guidelines.

Because the heater operates at mains voltage, if you are unsure, have an authorized AEG technician perform the repair.