Unit runs after water shuts off

Tipiford

We have a new Rinnai water heater model RL75 (new home construction) which the builder had set to 140º, and the warm water would run in the shower (and/or elsewhere) for a few minutes, then turn cold (this was not a constant, but rather, intermittent─and no codes observed). The building company's plumber said he'd never seen these units set on maximum before, and turned the setting down to 130º. We haven't experienced the cold water issue since, but we are seeing the unit run, up to twenty or so seconds after water is shut off. My question, then, is this a normal function of this unit?
Thanx

STEVEusaPA

Yes a normal function. You may hear the fan running during short uses of hot water to ensure their is hot water ready for use, and to clear all flue gases from the unit.

Tipiford

Thanx much