Seat Arosa cold start and temperature issues

That sounds familiar! I had similar issues with my Arosa, though it's not a diesel. The instrument cluster was acting up, and the engine was taking ages to warm up. Have you checked the basics? Is the coolant level alright? Any signs of a radiator blockage?

The coolant level is fine, and there's no visible radiator blockage. What exactly do you mean by 'basics'? Did your check engine light come on as well? What fixed it in the end? You mentioned the instrument cluster.

Yes, the check engine light was on too. By basics, I meant the coolant level and any visible signs of damage. In my case, the instrument cluster issue was caused by a faulty temperature sensor. Given your symptoms, I'd still suspect something in the cooling system, potentially the thermostat or a sensor. If you're not comfortable working on it yourself, a workshop is probably the best option. They can run diagnostics and pinpoint the exact problem.

Following your suggestions, I checked the fuses but found nothing. I took it to a workshop and it turned out my initial thought was right, the cooling grille was restricted. They also replaced a faulty sensor, and the total was 52€. The car seems to be running smoothly now. Thanks for the assistance!