Seat Arosa Diesel Auxiliary Heater Problem

Sounds like a pain! When you say it can't be activated, do you mean it doesn't even attempt to start or does it start and then cut out? Have you checked the coolant level lately? A low coolant level can prevent the auxiliary heater from working to protect the engine. It might also be worth checking fuses related to the car heater and ventilation system. Is your climate control working properly otherwise? Any issues with the heater core?

It doesn't even attempt to start, and my coolant level seems to be fine. Fuses all look good too. What do you mean by coolant level related to the error?

Okay, if it's not even trying to start and the diagnostic tool points to a heater error, then the glow plug is a very likely culprit. The coolant level is indirectly related; a low level can trigger a safety mechanism that disables the auxiliary heater. But if your coolant is fine, that eliminates that possibility. Honestly, replacing the glow plug on those heaters can be a bit tricky, and if you're already getting error codes, it might be wise to take it to a workshop. They'll be able to confirm the issue and replace the glow plug properly. Replacing heating parts without proper knowledge may lead to issues. Considering you have the parking heater, ventilation system, and climate control, I would seriously advise to take it to an expert.

Thanks for the help! I took it to the shop after all. Turns out you were right, it was the glow plug for the auxiliary heater. Cost me 440€ to get it sorted. Now I can finally enjoy a warm car!