Ok sometimes a blocked filter can cause that. But the E13 error code is something to do with the heating side of it.
Take the top off and look at the top of the door seal and on some models theres a NTC (temperature sensor) in there. Check the wires to it and make sure its not lose orbroke off.
If that's fine then remove the control board and inspect the board and see if theres a dry joint on there. If so try and resolder it and see how it goes from there.
Let me know what you find.
Thank you for the help you have given me. My machine is built in under a worktop unit, so therefore I am unable to take the top off without, apparently, pulling the machine out. As I am 80 and very fit I feel I cannot go further with your recommendations. According to my neighbour, who also has a NEFF machine, she has a little lever by which she can open the door in an emergency. Does my machine have such a switch?