Went down to the basement this morning and there was water on the floor; not much but a small puddle and a larger damp area, appearing to be coming from the water heater. Oh, no!
Shut the water valves, shut off the gas supply, called the plumber. Went back down to see what needed to be rearranged and/or moved to the safe...
...Took a closer look at the water and spotted the opened-up elbow in the air-conditioning condensate drain, hidden in the shadow of the water heater.
Y'see, the furnace guys didn't glue the joints in the PVC line; it has a couple of elbows in it and their reasoning was there no actual pressure on it and it's all the easier to clean out. This has worked out well. In fact, I had checked it back at the furnace end just last night -- which is when I probably disconnected that shadowed elbow.
I took a long look at the water heater heating element controls (gas), which is so slathered in safety devices it might as well be a fusion plant for all the sense it makes, and called the plumber back: "All I need is a relight!"
Sheesh. At least the water heater is up on little feet.
Update: Or maybe more than a relight! There was a leaking connection between galvanized and copper pipe, a previous homeowner not being in the habit of using (or requesting) dielectric unions when connecting dissimilar metal pipes.
3 months ago