My mom's house has two hot water heaters (duplex). The first I replaced 7 years ago and everything is fine. The second I replaced 5 years ago and the unions are very corroded.
The two water heaters are the same make. They use the same dielectric unions. They are both bonded. The both have anode rods installed. They both use the same city water.
The only difference is the newer heater has a blinking light controller the old one has a dumb controller.
The old heaters used regular unions and were not bonded. They had lots and lots of corrosion. After the first heater didn't develop any corrosion I figured that I solved the problem. I also don't see any leaks.
What could be causing this corrosion and how can I fix it?