Hello, I have a plumbing problem. I just replace the stem and the back nut thing that I needed to buy a special wrench to take out the old and install the new. That was about a month ago. No problems until tonight when I turned on the cold water in my shower. I got a pop sound (just once) and the water flow stopped. I kept twisting the faucet, and the water flowed again like there was never a problem. I repeatedly turned on and off the water with the same outcome every time. So my question is how do I fix this? Any suggestions would be greatly appreciated. Thanks in advanced.

Your terminology is not very specific. Sounds like you replaced the stem and seat in a compression valve faucet. If the seat does not have a snug fit in the threads, the opening and closing of the valve will work it loose and you can have problems like you describe. It depends on the specific design as to exactly what happens. I put teflon tape or some type of pipe dope on the threads before installing a new seat. That helps prevent the seat from loosening. It also prevents a drip from water going around the new seat. (I've had it happen.) It could also be the stem, there are some interesting designs out there.

Take everything apart, pay attention to how it comes apart and whether it is exactly as you put it together the last time. Probably not. Then put it back together with a couple wraps of teflon tape around the threads of the seat and possibly the screw that holds the faucet washer in place too.

EPMiller

Can you give us the brand name of the faucet. I assume it's a two or three handled valve and not a single handled one. DO NOT put Teflon Tape on the threads of the stem or the bonnet packing nut. You can coat the threads with plumbers heat proof grease for easy operation if you wish.

when I turned on the cold water in my shower. I got a pop sound (just once) and the water flow stopped..
You either have a small pebble in the cold water supply or the screw holding the washer has came loose and the washer's blocking the seat.
Shut the water off and remove the stem and washer assembly. Check that the washer's on tight. Now, with the valve still opened up, turn on the cold water supply to flush out the supply and the open valve body. Reassemble and test. Better now? Regards, Tom