Just in case no one has mentioned it-
Check your bypass valve(s)!!
Depending on your particular set up you can have 1, 2 or 3 valves.
All MUST be in the correct "summer" position.
If one or more are in the winterize/bypass position you will get a tiny
bit of warmish water then cold.
Your exact question comes up here fairly often and it's nearly always
bypass valves set incorrectly.
It could be faulty heat element/bad thermostat but that's much less
If you are un-sure of your valves correct position, take a picture of
the back of your WH showing the valves and post here.
We can probably tell you if they look right for hot water mode.