beko washer-drier door remains locked after cycle ends

My beak combo washer-drier WDIX7523000 is not working. The door lock remains activated for several hours following the completion of a washing or drying cycle. It is a hardly used machine, only 2 years old and just out of warranty.Turning off the mains and leaving a few mins resets the lock. However, this is not practical on an ongoing basis due to the position of the socketA local repair man has replaced the bimetalic door catch, and the main PCB. This has not sorted the problem. He did not think it was the air lock, as he disconnected the hose and blew through to clear it, and said that if the sensor was faulty, the machine would not be cycling through a wash as it stops the water inflow. He also disconnected the thermostat in the drying unit and that did not release the lock. I got him to stop working, as we seemed to hit a dead end