The short question is this: would a low-flow shower head cause some kind of increase in pressure to the water supply pipes that would cause a rupture and leak?
The longer story is this: I removed a previous stationary shower head and replaced it with this hand-held shower head (http://www.homedepot.com/p/MOEN-Propel-5-Spray-4-5-in-Hand-Shower-in-Chrome-26040/300676251). There was nothing unusual about the installation, it worked fine and there were no visible leaks.
About two weeks of daily use later the hot water to that bathtub faucet and only that bathtub faucet stopped working. A plumber came out and replaced the cartridge inside the handle (http://www.homedepot.com/p/MOEN-Posi-Temp-Pressure-Balanced-Shower-Cartridge-1222/202059049) saying that sometimes the temperature regulator inside the cartridge stops working, just one of those things.
Hot water had returned, we went back to daily use. About 4 days later we heard water behind the wall and found our downstairs bathroom below the shower in question was flooding from the ceiling. We turned off the main water and waited for the plumber to come back out.
He found that the cold water supply line to the shower handle was leaking significantly at a solder point. His initial diagnosis was whoever installed the line had done a bad job soldering the pipe and it had finally given out. He cut out the pipe and replaced it with his own, presumably superior, soldering job.
After he was done, as he was using the shower head to clean out the tub he mentioned how much he hated these kinds of shower heads because they restrict the flow of water so much, and that since "that pressure has to go somewhere" the new shower head was likely the cause of both the cartridge replacement issue and the later leak.
I would agree the shower head does not put out the most impressive pressure, but it doesn't seem anemic or problematic. I can't understand how a restrictive shower head could ruin a scald protector or supply line. Is this actually a thing? Should I look to replace my shower head, or was he just looking for something to be the cause that wasn't him? If not the shower head, could the cartridge be doing something that would cause the pipe to leak?
Best Answer
This is a fun question. I feel your plight and frustration. The answer is multi-point.
The TLDR version: Yes, a restrictive component upstream from your faucet control and the spicket can introduce the conditions needed for a leak between those two points.
When the faucet itself was off however, all of the water pressure in the home in the pipe is pushing on all sides of the pipe's and faucet's inner surfaces. Home water pressures can be about 60 psi (different codes in different places), but this PSI is regulated by a regulator on your main water supply. All the water in your home is restricted to whatever this is set at.
Now, when you open a faucet, you are giving that water a place to go. Think path of least resistance. The water goes there, but unless the pipes it is going through are too small (like a refrigerator water line) that water will come out at 60psi.
Suffice it to say for the example, the pipe between your shower handle and the shower head can handle say 40psi…. when you open the faucet, with no head, all 40 psi (nearly all), blasts out into the tub. Now put your thumb on it, and some MORE pressure pushes on the pipe sidewalls, while less than 40 comes out. Now put a low flow head on it, and even less.
So yes — if a pipe was weak to begin with, it can start leaking. Now, as far as the cold supply leaking because of the new head? BALONEY. Because when the water is OFF, it is seeing all of the pressure at those connections.
What is most likely the issue with the leak and the faulty faucet (I assert…) is that the act of you touching the shower head pipe had more vibrational impact on the overall piping installation. Also, calcium or other water impurities built up in the pipes may have broken free. This could be what caused the water mixer to "seize up" and also could be what weakened the pipes more than they were before you started the task.
How old is the house? These things do happen. Also, the plumber (while not at any fault), also jostled these connections, and he is right, if the job was lacking in quality, then everything you experienced could happen.