Phaeton Heater Core Flow Issues, Fix Guide

As someone with some hands-on experience working on VWs, I had a very similar issue with my 2014 Passat last winter. The car heating symptoms were nearly identical, weak heat output and error codes related to the heating system. After taking it to the workshop, they found that the electrical connection to the water valve had deteriorated, causing intermittent operation. This meant the engine coolant wasnt flowing properly through the heater core. The fix was relatively straightforward, they replaced the wiring connector and plug for the water valve, which restored full heating performance. Total repair cost was 95€ including parts and labor. The whole job took about an hour and the heating has worked perfectly since then. To better assist with your specific case, could you share: What error code are you getting? Does the heating work at all or is it completely dead? Have you noticed any coolant loss? Does the heating performance change with engine RPM? This information would help determine if youre dealing with the same water valve connection issue or if its potentially something else in the heating system.

Last service was just 2 weeks ago at 41856km and they did not spot any issues. But since then, the coolant leak seems to have gotten worse. I am now seeing drops under the car after parking. The engine coolant temperature gauge also fluctuates more than usual when idling. Based on your questions: Error code is P0597, Heat works but very weakly, Engine coolant level drops noticeably every few days, Heat output improves slightly at higher RPM Given these symptoms and the visible leak, I am starting to think it might be more than just the water valve. Could be dealing with a failing heater core or blockage somewhere in the system causing excessive pressure. Will have it checked out soon before any engine overheating occurs.

Based on those additional symptoms youre describing, especially the visible coolant leak and fluctuating temperature, this does sound more serious than the electrical valve blockage issue I had with my Passat. The combination of symptoms youre seeing strongly suggests a physical failure rather than just an electrical connection problem. When engine coolant is actively leaking and the temperature gauge is unstable, theres likely a compromised component in the cooling system. Your P0597 code typically relates to thermostat heater control circuit, but the visible leak points to a mechanical issue. From my repair experience, the weak heating combined with coolant loss often indicates either: A failing heater core, A crack in the water valve housing, A blockage causing excessive pressure in the system Given that youre seeing drips under the car, Id recommend getting this checked immediately. My repair was a simple 95€ fix, but if coolant is leaking near hot engine components, you could face more extensive damage. Would definitely have a shop pressure test the cooling system to pinpoint the exact location of that automotive valve or component failure. The fluctuating temperature at idle is particularly concerning as it could indicate air in the system from the leak.

Thanks for the detailed feedback. The situation does seem more serious than I initially thought. Seeing actual drips of engine coolant under the car definitely changes things. I will get it into the shop this week before the cooling system issues potentially cause any engine overheating. I will have them do a full pressure test to track down that leak. The intermittent temperature fluctuations and weak car heating make me think the leak could be allowing air into the system. Better to fix it now than risk more extensive damage. Will update once I know what component was actually causing the coolant leak and what the final repair entailed. Really hoping its just a cracked water valve housing and not a full heater core replacement. But either way, it needs immediate attention given the active leak.