Armed with more information than I had this morning, I went out to the water heater panel this afternoon, pulled some leads, cleaned, them, and reconnected everything. I now have HOT water again. YAAAAAY.
But a new thermostat and ECO thingamabob are in my future. They are cheap parts that are obviously about to fail, so I might as well switch them out.
(One of my favourite scenes in the movie Penny Serenade is when Roger and Julie’s friend Applejack arrives in California from New York. Their newspaper printing press is jammed and the bathtub is clogged. Applejack barely greets anyone before giving the printing press a kick, which starts it up, and then says, “Now, where’s that bathtub?” He is hailed as a miracle worker.)