This weekend, while getting ready to leave for a business flight to Boston, I decided to take a shower. Karma decided that this was a regrettable decision, and my hot water suddenly became so excited to escape its pipes that it began coming out of the hot water knob, rather than waiting patiently for its rightful point of egress at my shower head. I was chagrined.
In the documentary version of this node, the true story of how my back gave out five minutes later is also covered, but for the sake of factual brevity, I will eschew that delightful sub-plot. Let it suffice for me to say that Sunday night was not my night.
While desperately holding the loosened knob against its casing, lest hot water spray out and mar my boyish good looks, I called the repair guy on my cell. (The documentary version, by the way, also explains how I actually was unable to contact the first repair guy, so I had to call my landlord and wait for him to call the other repair guy, who arrived mercifully soon. But, that wouldn't be fully relevant to the resolution of this particular problem, so I won't go into it here, of course).
Fortunately, I was blessed with a repair guy who not only arrived in record time, but saw fit to explain what went wrong, and how he stemmed the flow of disaster. Because I am a benevolent, patient man, I thought it might be nice to spread the knowledge here. It is likely that one or more important details were lost between the repair man's lips and my typing fingertips, so if anyone out there in the nodeverse knows better, please murder my ignorance with information.
The problem was that my hot water knob was tightened too firmly the last time it was turned off, so the next time I tried loosening it, the entire valve loosened with it. The band-aid solution was to turn off the hot water, which actually proved difficult: My hot water's turn-off valve had no handle, so turning it off required fastening a wrench to the shaft and spinning in circles until the flow had stopped. (See the documentary version for how much this freaking hurts to do with a pinched nerve in your back.) It's probably a good idea to make sure you know where your hot water turn-off valve is, and to verify that it has a handle. You can get one at Home Depot if it doesn't.
Repairing the actual knob first requires removing it from the valve system by unscrewing the central screw (sometimes protected by a cap that would require a wrench to remove). Once the handle is off, you can re-tighten the outer fittings that were loosened by the overzealous handle thread, and you'll be good to go. If your handle feels loose or shakey when you turn it, or if it takes many turns to get water pressure, this fix may also work for you.