Water heater inlet corrosion after 4 years? Installer claims they did everything right
My educated guess without being there is that the flex connector joint was not installed correctly or is just leaking. I never liked this type of installation since it was made for the novice and not a professional. I always used hard copper and a non-lead solder containing silver. I also never used galvanized piping, just brass fittings and copper tubing. Whoever installed this did a sloppy, non-professional job.