I just had to replace (under warranty) after two years of use the electronics and flush valve of my Neorest 500 due to hard water scaling issues.. I guess things got plugged up and water got onto the electronics.
I am not sure, but I heard that water around here is 18 grains per gallon and I guess anything over 10 grains is considered hard water.
I am currently looking into solutions to keep this from happening again in 2 more years. I currently have no water softener at all.
According to my fire sprinker system my water pressure is 60psi which is within the neorest 500 spec.