This "6 year" hot water heater failed after 3.5 years - is it bad luck (eg normal for the $429 box store 40 gal DHW heaters and how they make money off what I expect is a pro-rated warranty?), poor water and/or pressure environment for the heater, or possibly an installation issue?
The failure is a pinhole leak about 1/2 way up the tank (I could hear a hissing when the tank has water pressure.) After turning off the cold water supply, hissing stopped, but upon turning back on the leak became worse, even when supply was turned off, requiring immediate draining of the tank
Some facts about the water and system:
Well-pump with cold water pressure tank - which takes care of thermal expansion. However, the pressure switch is likely operating in the 20-40psi range. Could this pressure cycling, 100-500 times per day, weaken the tank? (100 times per day is probably normal, but in the summer could approach 500 times per day due to use of garden hoses.)
The well water is rather acidic, but a solution pump raises the pH to the low 6s. The water is naturally soft enough, with no other conditioning.
Never observed any excessive discoloration of the hot water.
The shower is over the heater, and on occasion, there is some air in the lines - don't recall if it was hot or cold. Interestingly, this hasn't been happening for the past ~1 year.
A sand filter was NOT used water supply for most of the duration. Possibly a fair amount of sand went into the tank - based on the amount of sand in the tank of a nearby toilet.
The previous two hot-water tanks had also been replaced prior to warranty expiration (under the previous owner), but the last one failed (3.5 years) due to internal gas leak instead of water. (I prefer the internal water leak failure than as gas leak on New Years Eve!)
Facts about the installation:
Connections : Flue, plugged into grounded AC outlet, gas supply, hot and cold dielectric w/flexible water pipes, tanks metal feet rest directly on the concrete floor
The water pipe connections are via dielectric fittings at the tank, with ~18&24" flexible hot watcher hose kit to the copper pipes. I'll put photos up.
Cold water pipe has nearby electrical earth ground connection, but the tank itself has no direct connection (except possibly the flexible hoses and AC plug ground)
After 3.5 years there was some corrosion on the hot water side, and the fittings can't be removed from the tank.
Previous tank was ~4' on resting on concrete blocks so I replaced with a tall (~5') and modified the plumbing using the flexible hoses instead of direct copper connection
Never checked the anode rod, maybe I should?
With 50 degree well water in the summer, everyone would be happy if the next one lasted longer.