tub and shower faucet or just a shower??
you probably might just want to take the shower head off
and see if it is clogged up first....
the 1300 cartridge is pretty easy to change and most likely
either the hot or cold side of htat valve has clogged up with
something, basically shutting down the valve...
pull the cartridge out and get another one $35+
blast out a stream of water first before installing the new part
to be sure that their is no sediment hanging around in the valve body
Please note that
the 1400 can be an absolute pain in the ass to get adjusted properly...
I just tangled with one last week.