Single knob shower faucet produces only water.
It was installed in this condo about thirty years ago.
It no longer 'produces' cold water (except for s short period after is is turned on and the hot water 'reaches' our condo).
One plumber 'scraped' a cartridge, which seemed to work but not for very long (a matter of minutes). The next plumber said we needed to replace the valve, tear up the tiled wall, etc.He said 'the little notch on the cylinder wall, which stabilizes the ball was worn away....."
I am handy enough to try to 'fix' it myself. It looks to me like it is a replica of the Delta single handle kitchen sink, which i repaired myself (with a little kit from our friendly hardware store).