Shower With Low Pressue
All of my faucets/shower heads have great pressure, except one. The hot water in the one is very weak, and the cold is not much better. From wat I can see in the basement, the lines are Pex.
Is there an easy way to diagnose/fix this, without opening the wall?

Buy a pressure gauge and some adapters / hoses. 

Remove the supply hoses at the offensive faucet and check the pressure at the shutoffs. 
Check another , good faucet’s shutoffs and compare. 

You mentioned PEX, why ?  Is it only those lines that are PEX ?  

Pressure shouldn’t be affected much by pipe material choice.  Flow rate is somewhat, but you didn’t say that.  

You can also pull the faucet screen and cartridge(s) to see if they are clogged.  Is the faucet new? Is the problem new ? Is it the same kind of faucet as everywhere else ?
First I would check to see if there's a flow restrictor in/at the showerhead. Basically it's a thin plastic washer with a very small hole. Next, on some better quality shower valves there are shut-offs located behind the trim; these could be partially closed to save water. Now on to the PEX. PEX comes in two basic flavors; "A" and "B". PEX-A is expanded and quickly pushed over the fittings, where it (and a PEX band) then contracts around the fitting. PEX-B fittings slide into the tube and a copper or stainless steel ring is then clamped around the tube. Basically this means that the i.d. of "A" fittings is larger than "B" fittings.  I have seen first hand where a 1/2" male adapter on a tub/shower valve along with a 1/2" "B" 90* for the spout restricted the flow enough that water would flow out the shower head when trying to use the spout. Copper fittings go over the tube so the i.d remains the same or larger.

On a similar note; push to connect (i.e. Shark-Bite) fittings also go over the tube so they don't reduce the i.d.. I'm not saying you should bury these types of fittings in a wall because that would just bring up an argument that's already been beat to death. They did solve my problem over 10 yr.s. ago. I think they can just call a Plumber if they ever fail. The fix would be 1/2" copper pipe and copper fittings. Most likely the fittings will be ProPress; fittings crimped onto the tubing (vs. a sweat joint) with the same type of rubber O-ring seal that was in the Shark-Bites.
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Although this is not common sometimes there is a buildup of particles in the valve cartridge. Shut the water off remove and inspect also while it is out,  barely turn the water on to  flush out the valve body.
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Take off the head and try it. They clog. I'll betcha that's it. If not, take off the escutcheon plate. Some mixing valves have adjustments and some have rubber restriction plugs (for lack of a better term) under brass plugs. They limit water flow. Take them out and put the plugs back in. See what happens. We're on well water so only have about 45 psi. I took the rubber plugs out and it helped. It could be the mixing valve(s) themselves.

It's rarely a pipe issue, almost always a shower head issue. Especially with the bigger heads. The holes in them tend to be small and plug up.
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I agree with the others, take apart what you can and clean it. Also, the first thing I usually do with any showerhead, be it mine, hotel, VRBO, friends, neighbor's, in-laws, is break out my Leatherman, take the head off the spout and rip out the restrictor plate. Have you done that?
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(01-02-2023, 11:58 PM)MstrCarpenter Wrote: On a similar note; push to connect (i.e. Shark-Bite) fittings also go over the tube so they don't reduce the i.d..


Shrkbites also reduce the i.d. of a pipe.   Take a look at one again and notice the male portion inside the fitting that slips inside the pipe.
Thanks everyone. I’ll try cleaning and see what’s in the shower head.

(01-03-2023, 05:11 PM)David Stone Wrote: Thanks everyone.  I’ll try cleaning and see what’s in the shower head.

Your previous, multiple threads confused me a bit last nite, I thought you were asking about a faucet.

You should probably pull the valve cartridge to check for debris there.   I rented a brand new house in college that had a similar condition and when they pulled the valve they found a ziplock baggie in it
I soak our shower head in LimeAway periodically. It has a pulsating setting(dial) that ceases to pulsate and needs cleaning. We have a water softener, but the shower head still clogs.

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