Audi S4 Heat Failure Points to Faulty Heater Valve

I had a similar issue with my 2007 Audi S6, and as someone with moderate car repair experience, I can share what worked for me. The symptoms were exactly like yours, poor cabin heating and error codes. After inspection, it turned out the electrical connection to the water valve was faulty, affecting the engine coolant flow to the heater core. The repair cost was 95 Euro, which covered the replacement of the wiring harness and connectors. This definitely needs attention because: A malfunctioning water valve can indeed lead to engine overheating, Poor coolant circulation can damage other heating system components, The issue typically worsens over time Before suggesting specific fixes, could you share: Current engine coolant temperature readings? Does the heat work better when driving versus idling? Are you noticing any coolant leaks under the car? Which specific error code is showing up? These details would help determine if your issue matches what I experienced or if there might be other factors involved.

Last serviced 2 weeks ago at 171485 KM. Thanks for the detailed response. The coolant temperature stays normal around 90C, and yes, the heat works slightly better when driving. No visible coolant leaks under the car. Getting error code P0597. After checking the wiring with a multimeter, I found the heater core gets flow, but it seems inconsistent. The water valve appears to be sticking intermittently. Was your repair just the wiring, or did you end up replacing the actual valve? The 95 Euro cost seems low compared to what my local shop quoted for a full water valve replacement. Would it be worth trying to clean the valve first, or is replacement typically the safer bet with these engine coolant flow issues?

Thanks for those additional details. Your symptoms match my experience even closer than I initially thought. While my initial repair focused on the wiring, the inconsistent flow you described ended up being temporary fix. Two months later, I had to replace the entire water valve assembly as the valve itself was indeed sticking. The full water valve replacement ended up costing 320 Euro for parts and labor, significantly more than just the wiring fix. However, it completely resolved the heating issues and prevented potential engine overheating problems. Based on your description: Normal coolant temperature but inconsistent heat flow, Error code P0597 indicating control circuit issues, Better performance while driving, No visible coolant leaks I would skip attempting to clean the valve. In my case, cleaning provided only temporary improvement, and the automotive valve eventually failed completely. The sticking behavior you describe typically indicates internal wear that will only worsen over time. The proper fix is replacing the water valve assembly. While more expensive upfront, it prevents recurring issues and potential damage to other cooling system components.

Thanks for the thorough explanation about the water valve issue. This definitely helps narrow down my problem. Looking at the cost breakdown, the 320 Euro quote from my shop for a complete valve replacement seems reasonable now. Given the sticking valve symptoms and the risk to the cooling system, I agree that trying to clean it would likely be a waste of time. Better to fix it properly now than deal with bigger problems later. The fact that your car had such similar symptoms and the replacement solved it gives me confidence this is the right repair path. Will schedule the water valve replacement this week. Really helpful to know that trying to save money with partial fixes like cleaning or just electrical repairs might not be worth it in the long run. Not worth risking engine coolant flow issues or potential overheating just to save a few Euro now.