School plumbing service. In a closet, there is a hose with a shutoff valve for both hot and cold water lines; both are open. When the valve is off, this will create a crossover from hot to cold. The same is true with the kitchen pre-rinse hose if the hot and cold water lines are open with the sprayer off. I also looked at the water heaters and advised that the cold feed may need to install a check valve.