Bad Check Valve????

[exav8tr]

I think I just had my hot water check valve go bad. DW just turned hot water on and heard a, barely negligible thump, and no hot water..In looking at the hot water heater, there is a brass valve for the hot and one for the cold, which I take is the intake. Is it possible both have gone bad Should I replace both Are they available at Home Depot or do I need to go to a RV supply store

Any help would be appreciated, DW likes her hot showers daily and I like her to like her hot showers...