When does a water heater become a boiler??

We are working on a 70,000 sq.ft. nursing home. There are two high temp, high capacity, gas fired "water heaters" that supply hot water for a commercial kitchen. I'm not sure yet if the domestic hot water is tempered off this supply or it may be completely separate.

The plumber had a boiler inspector on site last week and the inspector said that remote shutdowns will have to be provided for these "water heaters".....he called them boilers.

I have had to provide remote shutdowns for large boilers that provide building heat, but haven't had to do it for these smaller units. And of course in isn't engineered into this project so there were no rough-in's provided for the shutdowns.

When does a water heater become a boiler?? What is the difference?

thanks,
GJ