GLE diesel cold starts rough heat not working

I am familiar with this predicament. I drive a GLE as well. The symptoms you describe correspond to a defective PTC heater, which is an electrical auxiliary heater. The HVAC system relies on this heater to provide supplementary heat, especially during the engine's cold start phase. An electrical fault in the PTC heater would indeed cause diminished heating performance and potentially affect engine management, which would explain the high fuel consumption. Have you observed any unusual electrical behavior from other car systems

No unusual electrical behavior. Just the heat not working and rough cold starts. How sure are you about the PTC heater

While a definitive diagnosis necessitates a thorough inspection, the convergence of symptoms and the stored error code strongly implicates the PTC heater. It is conceivable that other components within the HVAC system are contributing, but the heater is the primary suspect based on the presented information. I recommend consulting a qualified technician for a comprehensive evaluation. Expect a heater repair cost in the neighborhood of 350€.

Thanks for the info. Workshop confirmed PTC heater is faulty and quoted 350€, so that lines up. Replacing it.