What happens when the sprinkler and Hydrant centrifugal pumps runs continuously in the closed piping system with out any water discharge as the valves and the complete system is closed.

What happens when the sprinkler and Hydrant centrifugal pumps runs continuously in the closed piping system with out any water discharge as the valves and the complete system is closed.
There should be a discharge, when pump keep on running with out discharge, the water at the pump would heat up and turn into steam and cavitation,. when properly install/design a high temp release valve would release the hot water