I first encountered formic acid erosion/corrosion when our installed air conditioning and heat pump evaporator (indoor) coils began suddenly leaking refrigerant in 2008. These were not old coils either, and some had only been installed for a year when the issues arose.
My grandparents lived in Saint Clair, Pennsylvania, which is in the heart of the anthracite coal region. Pop-Pop had a Westinghouse Appliance store and serviced everything they sold. In addition, he had helped to wire homes when electricity first became available and serviced lots of coal boilers.
When I first entered the trades in 1972, residential tank-style water heaters shipped with the aquastat set to approximately 140° F. Dishwashers had no need to incorporate a sanitizing cycle. Around 1977, water heater manufacturers were required to lower the aquastat temperature setting to approximately 120°, and now, dishwashers needed to incorporate a sanitizing cycle where rinse water in their reservoir was raised to 140° or higher.
When I first entered the trades, F. W. Behler installed lots of galvanized and copper spouting. I was not keen on working several stories above terra firma, which hampered my speed in getting-er-done. What to do to overcome my fear of heights? Go skydiving of course!
When our local water company started adding Watts No. 7 dual-check backflow preventers to all water services, we soon discovered water heaters were failing at a rapid pace, with gas fired models exhibiting telltale signs where the cold/hot water lines skewed off making them look like a bow-legged cowboy!