First unplug machinen. Take the bottom panel of the machine off (screws are on the bottom) and reach up inside where the door lock is. There is a ring at the bottom of the lock mechanim, pull on it and door will unlock.

Same problem with my 6 year old machine. Replaced k1 and k4 relay on ccu board. Now 3 weeks later all is still working fine. Problem looks like design error. When door latch opens the latch coil generates a voltage spike that arcs cross the relay and eventually the contacts don,t hold, especially at the vibrations generated during the final spin cycle. F11 error is just a bad diagnostic.