Aygo rear window heater failure

I had a similar problem with my old Renault Megane. Rear window heater stopped working, and it turned out the battery was heavily discharged. The car's computer system prioritizes essential functions, and heating is often one of the first things to be cut off when the battery voltage drops too low. Have you checked your battery's condition?

Interesting! So, a weak battery could actually cause the rear window heater to fail completely? I'd have thought it would just be less effective, not just quit. Is that really how it works?

Yes, on the Megane, the rear window heating was disabled completely due to low voltage. Modern cars are full of electronic control units (ECUs), and they are very sensitive to voltage fluctuations. If the voltage drops below a certain threshold, the ECU might disable certain functions to protect the system. I would strongly suggest having your battery tested, and if it is indeed the culprit, replacing it. Otherwise, you may need to visit a workshop.

You nailed it! Took the Aygo to a shop, and they confirmed a heavily discharged battery was the culprit. New battery fitted, rear window heating's back in business. Total cost 290€.