Warranty claim voided

Our leaking geyser is still inside the 10 year warranty period. Much the same as everyone else, I was given bizarre reasons for the warranty to be voided. My plumber explained to me that the installation was compliant at the time the geyser was installed, but compliance rules have subsequently changed. Duratherm are ****** and will make up any excuse to void their warranty. I am going to fight them tooth and nail. The can’t wriggle out of their liability so easily.