Mercedes SLC diesel heater issue resolved

I had a similar problem with my 2018 BMW 3 Series. The heater was blowing cold air intermittently. The issue turned out to be a faulty thermostat, which regulates engine coolant flow. Have you checked the thermostat's operation? A malfunctioning thermostat can also cause issues with the car heating system and store error codes.

Thanks for the tip. The error code specifically mentions the water valve, not the thermostat. However, is there any way a faulty thermostat could indirectly trigger an error related to the water valve, maybe by affecting the overall engine coolant temperature regulation?

While the error points to the water valve, a faulty thermostat impacting engine coolant temperature is plausible. In my case, it was like a domino effect, one failing component affected another. Given the complexity, I'd suggest a workshop visit for a thorough diagnosis. They can pinpoint the root cause and prevent further issues.

Understood. Thanks for the analogy and cautious advice. I appreciate you sharing your experience. I took it to the workshop, and you were right, the thermostat was defective, even though the error code pointed to the water valve. The mechanic replaced the thermostat and the water valve which he said was corroded. Now the car heating works perfectly again!