The fan continues to run after the micro wave oven is turned off (Miele M626EG). It only stops when the door is open and as soon as we close it it starts again. The error suddenly started this morning and we had to unplug the power cord to get the fan to turn off while the door is closed. We've had the same oven for several years without any problems and never had this issue before. We have tried everything without being able to make it stop. How can this be fixed?