I bought tank less heater from Amazon, the tank less heater has 240 Volt, In Los Angeles most have 120 Volt friend of my mine put extra wire make 3 wires to run the 240 Volt but the system of tank less heater did not work giving error of H6 not proper electric , have no idea what to do and how to fix .

I like to see the system first working or not ? how because he said that the system have fault , i call company they said there is not enough electric giving code error H6 please advice what to do.