F13 suggests a fault with the heater element, located at the front of the machine. If, if the heater element fails, the wash will suspend after the second contrarotation stage.
You can try what is in our manual first:
1. Switch off the power using the 'MAINS ON/OFF' button
2. Press and hold the 'Temperature' button
3. Carry out the next three steps within 3 seconds;
4. Switch on the power
5. Release the 'Temperature' button
6. Press the 'Soil type' button
7. Check that a message similar to "DIAGNOSTIC MODE 123F7F2F5V127" is displayed. If it is not, repeat from the beginning
8. Switch off the power
9. Switch on the power. The fault code should have cleared
This is from an engineer guide we have rather than actual experience I might add.