My work had a dishwasher that performed terribly when we first moved in. About 6 months later we complained and they replaced it. Worked slightly better, but still sub par (dishes came out gray with bits of food still on them, with or without prewash). About 6 months later, the water heater leaked and had to be replaced. For the past year since then, the dishwasher works amazing (no prewash and dishes shine). I don’t know what transpired to cause the change. I was guessing that somehow the aging hot water heater just leached too much mineral into the water or something that the soap formulas could not overcome?

tldr sometimes it really does just seem like superstitious voodoo is really what matters with dishwashers

Water heaters have different temperature settings that are supposed to be adjusted depending on the occupants of a building in order to avoid scalding.

The old water heater was probably set to 110°F or something, and the new one to 140°F.