I need some opinions here. I was engineer of record for a restaurant a couple years ago. They requested instantaneous gas water heaters and I specified them. Apparently the warranty for one I specified is only good for residential installations. Fast forward two years the stupid thing fails and needs to be replaced. The plumber tells us all this yesterday. The architect is telling me I owe them a water heater. Is he correct? What, if any, leg can I stand on to refute this?