Send for warranty. Don't be a stupid hero trying to do something stupid.
Unless you want your name to come out in the headlines next day.

If wiring problem, it will directly trip and no lights at all.
Got lights means it is working are something failed inside. If water flow ok then it will be more serious issues.
So, asking the installer to check will be the safest way.
Changing a fuse in the main board I dare to do, changing plug's wiring piece of cake. Changing the ceiling fan also no problem.
But not instant water heater.