OK. Do you have good pressure to your bathtub spigot? When you removed your shower head, did you turn the water on and see what kind of pressure you had coming straight out of the shower pipe with no head on it? If you have pressure everywhere, you may just have a clogged up shower head. On a lot of low flow heads, sediment from your pipes, water heater and just from the city water supply, as well as hard water build up can block the shower head. If so, take the shower head apart and clean all the parts. I use a large needle to pick the grit out of the fine ports on my heads. Depending upon your shower head, screws are sometimes hidden under plastic caps. The removal of the screw allows you to break the shower head down. If you can get the schematics for your shower head, it makes it easier. After getting all the grit out, I soak the parts in vinegar or a lime dissolving solution. Be careful with yours so that you do not harm any finishes. I hope this helps.
Low water pressure from every orifice in the shower with all fixtures removed, even one by one, whether it's coming from shower with head removed, or tub spicket. While I had all of this out, I soaked the shower head in a bowl of CLR for a very long time also, but the pressure is the same with it installed or not.
Like I said, I even sprayed the CLR in through the shower pipe to clean diverter valve and nothing has changed. I was thinking that part of the missing rubber washer got stuck in the center of the diverter, so I also removed the tub spicket and ran a piece of .032 stainless safety wire with a hook on the end inside and found nothing.
I'm puzzled for what to do next because like I said there is pressure everywhere else in the house. Looked at plumbing behind tub and can't see any exterior damage to the pipes inside the wall. The plumbing does change from copper to that vinyl white tubing going up the wall to the attic, but still no exterior damage or kinks.
When you removed the individual stems, etc... to flush everything, did you have good water pressure? What make, model and manufacturer is your shower/tub valve?
Prior to the water not shutting off the water pressure was better, but still not good like it should be. Like I said, it was great when I first bought the place 4 years ago, but has gotten worse in the past few months. After the hot water wouldn't shut off about two mornings ago, and I had to pull the stem to find the screw and rubber washer laying inside, which is why it wouldn't shut off. All that was left of the washer was about the size of the screw head, but was swollen, so the outer portion of the washer is missing. I installed a new washer and that fixed the problem with the shut off. After the repair is when the pressure became almost non-existent. This is why I'm thinking the missing portion of the washer could possibly be what is clogging the center of the diverter.
I know the fixtures are something common that starts with a P, can't remember what they said it was at Home Depot...Puritan or something. The guy said that they were very common though.
I have access to the back where the pipes are through a cut out in the next room. I guess I'm planning on investigating the attic first to see if I might have a pinched or kinked vinyl tubing or something. At that point if I don't find anything obvious, I guess I will desolder the diverter, attach a piece of tubing to run to the tub, and turn water on to check pressure. If I have good pressure, I guess I'll be replacing the diverter if I can't get it cleaned out.
Does it sound like I'm on track? Believe me removing and replacing that diverter is the last thing I want to have to do. Been a few years since I've soldered copper, but I was pretty fair at it. Just kinda a tight space to be working. If you have any other ideas I am open to try anything before that.