No. of Recommendations: 3
Interesting update.
So I cleaned out the water heater (incorrectly, but that's a different post). Because I had a valve on in the house (incorrect!), the house lines drained. When I was done, I closed it, reactivated the water heater, and after some burping at the taps, water flowed. Including at the shower. Either some debris was dislodged when the lines drained, or some sort of air bubble was "stuck" in there. Either way, hot water is flowing again.
And next time I know how to drain a water heater...had to plumber out to deal with a different problem (warranty), and he verbally told me what I was doing wrong.