nicktheplumber
I presume that you’ve tried cleaning the shower head. If you take off the shower head does the water flow well through the shower arm? Since you have separate cold and hot valves, I assume that you have a simple mixer valve (i.e. not a diverter valve assembly) in the wall. If the set-up is >40 years old, you probably have galvanized pipe, which is subject to scale buildup.
It is hopeless to try to snake out the shower head supply pipe…I’ve never even tried to do that. Even if you could get a snake into a 1/2″ supply pipe, you’d never get it to make a 90 degree turn into the mixer valve. If you have scale in the pipe at the valve, you might be able to scrape it out with a short piece of wire.
NtP
