Sorry, have to agree. You really cannot get any more basic than a water heater, and if you are struggling to understand how they operate I suggest you get an old one and rip it to bits while it's disconnected rather than play with one in situ that belongs to someone else.
I know it's not very constructive and that these things are maybe not as common as they used to be, but basic engineering principles should see you right on diagnosing the fault, something that they don't teach in college enough?
Your obviously enthusiastic to progress so you'll learn quickly given the right opportunities, but going it alone without the right technical knowledge isn't the way to do it.
Just to add, no one is having a dig at you personally, but in a few years time you'll appreciate how little they teach you to get you through an exam, it's the colleges (or should I say the certification bodies) fault not yours, just know your limits.