Error code EF9 on your AEG washing machine indicates a problem with the heating system. Here's how you can fix it:
1. Disconnect the washing machine from the power supply.
2. Check the heating element for any visible damage.
3. If damage is found, replace the heating element.
4. If no visible damage is found, use a multimeter to check the resistance of the element. If the reading is not between 20 - 50 ohms, replace the element.
5. If the heating element is functioning properly, the problem could be with the wiring or the main control board. In such a case, it is recommended to call a professional technician for further assistance.