Hi, my 2015 vrs TDI is losing coolant started off slowly now it's every few days couple of hundred miles. No signs of leaks oil looks fine new tank put on, no white smoke engine sounds fine not rough at idle. Water pump done at 80k now sitting at 119k. Has anyone any ideas

EGR cooler, does your expansion tank smell like exhaust?

I would suggest that the cap to the header tank has failed. The cap has a spring in it and stops the pressure in the cooling system getting to high. What seems to happen with the pressure caps on Mk7 cars is that the caps fail and they leak coolant out of the overflow. A (revised) cap from a MK7.5 should fix the problem.

Mechanic has told me it's either the egr or the head. Exhaust gases in the coolant

Ask your mechanic to reroute the coolant hoses to bypass the EGR cooler temporarily to rule that in or out.