Plumbing Questions? Ask a Plumber and Get Answers ASAP.
Turn on 3 hot water taps, tell me if the heater fires up or not.
If it does not fire up
Please attach a well focused, close up photo of the wiring diagram glued inside the service panel,you can use the paper clip-icon at the right end of the toolbar at the top of this dialog box.
If there is no paper clip-icon, look for the '+attach files' link at left of your send button.
I can mark it up with trouble shooting instructions. You will need a multi meter ($30 at a hardware store) and some experience working with appliances, let me know a lot about your skill sets in those regards.
We can go from there.