F21 is a motor related fault. But lets try reset the control and see of it clears the code from there. Its as below.
To reset it.
Turn the appliance knob to the off or reset position, 12 o'clock.
Turn the knob to the 6 o'clock position.
Press and hold the spin button.
Whilst holding it, turn the knob to the 7 o'clock position.
Continue holding the spin button for about 5 seconds.
Release the button.
Turn the knob to off.
When your turn it back on it should have cleared the error code.
Then retry the washer and see how it goes. If it doesnt reset or the code comes back again then you need to remove the motor and at the back either side are the cabon brushes.
You need to take them out and see if they have worn down. If so then you need to replace them and that should cure the fault from there.
If you need anymore info just get back to me.