A bit of back story: I’m a second year apprentice and my foreman has probably 15 years of experience, I have never seen this guy not be able to solve a problem or trouble shoot something. Today we installed a simple 120v outlet coming off of a 15 amp breaker in a sub panel for a tankless water heater. We metered it and everything checks out. When we unplug the tankless heater from a different outlet in the room to this one, it will not turn on but if it is plugged back into the original outlet it is fine. It almost seems like we have a dropped neutral but we have confirmed about 4 times over that, that couldn’t be the issue. We’ve also changed the outlet out itself 3 times and metered it each time. We’re both completely stumped as to what it could be sp any advice would be appreciated.

The water heater requires 120V and less than 10 amps to run as a heads up.