Navien review: Useless warranty and no customer service

I had a tankless hot water system installed in 9/2022. It has been maintained twice a year by the original installation company. 4 years later the system is totally rusted out and does not work. I live about 8 miles from the ocean. The unit is installed in a corner of the house under cover so it is protected on 3 sides and above with tall bushes on the 4th side. We contacted Navien and their warranty department said the problem is caused by salt erosion and therefore not covered by warranty. We were not allowed to speak directly to the warranty department to explain that we are not in a salt environment. Their warranty is useless; their customer support is worse that useless. I now have to pay to get a new unit installed (it will not be Navien for sure) and take Navien to small claims court which I intend to do.