What better place to be on a cold snowy day than lying on my side in a crawl space under my porch, in a muddy pool of water, getting sprayed on my glasses until I could hardly see. Yes, I had a plumbing disaster today, though I was able to fix it without waiting for a plumber or wasting hours of running water. Seems that somehow, whether influenced by the cold or what I don't know, an "T" on the pipe going into my water heater started leaking out of an unused fixture. I couldn't find anything that could have been blocking that before, so how it suddenly started gushing water I don't know. It was easy enough to screw in a pipe plug and fix it.

It's amazing how closely the process of fixing plumbing parallels fixing a software bug.

• At first there's some weird problem -- my hot water heater seemed to be making a loud hissing sound.
• Various things are tried to work around the symptoms -- I turned off water to the heater, and turned off its pilot but the problem persisted.
• Experts are pulled in and incoherent problem reports are given to them -- I called my dad and a plumber, and blathered to both at various points, with speculation and bad observations.
• Other parts of the system are observed to try to narrow down the problem -- I watched my water meter spin (and stop, and spin.. weird..), listened to pipes to figure out where the noise was coming from, and eventually discovered the sound of a waterfall underneath my floor.
• When the actual cause of the problem is finally identified, the actual process of fixing it is often amazingly trivial after all this -- and so I found myself in my crawl space, looking at water streaming out of the pipe, and screwing a plug into the hole. A 1 line of code type fix..
• Fixes sometimes just fix the symptoms -- why did that thing suddenly start leaking? Did it have to do with the low temperatures? Until I know the answer to that, I can't consider this "bug" definitively fixed.

Update: It was probably an old pressure relief valve that failed somehow.