There is, once again, hot water. Fixing the problem involved two things: a new thermocouple and a new valve insert of some kind. Total parts cost was only $10, so that's not so bad. The plumber mentioned how annoying it was that whoever installed the existing water heater used all rigid pipe for both water and gas, making replacement a real pain. He said it would cost $900-$1100 to get a new one put in. But luckily, he said I don't seem to need a new one. We didn't hear any indication that tank fouling was getting to be a problem, so it probably has years of life left.

By the time I get home from work, I should have 50 gallons of piping hot water at my disposal and it is my full intention to take the longest shower ever.