Seat Arona Diesel Heater Problem

Sounds familiar! I had a similar problem with my Arona's heater last winter. The air circulation was all messed up, and the windshield fogging was a nightmare. Have you checked the cable and plug connection to the flap motor itself? It's a bit of a pain to get to behind the dashboard panel, but that could be the culprit. Does the temperature regulation work at all, or is it just weak no matter what setting you use?

Where exactly is that flap motor located? Is it something I can access without taking apart the entire dashboard? Also, does it affect the heater core's performance directly, or is it more about directing the airflow?

Yeah, mine was doing the same thing. The flap motor controls where the air goes – windshield, feet, face. If it's stuck, it won't direct the hot air properly, hence the weak heat and windshield fogging. I wouldn't recommend tearing into the dashboard panel yourself unless you're really confident. You could accidentally damage something else. Better to have a workshop take a look, especially if you suspect a loose connection. They can diagnose it properly and fix it quickly.

Took it to a workshop. They found the error code, checked the connections as you suggested, and yup, a slightly loose plug on the air distribution flap motor. 95€ later and the heater's blasting hot air again. Thanks for the heads up!