If the water going to the valve is not hot enough, messing around with
the valve is not going to solve anything. First thing is to check the
temp at other faucets-- with a thermometer-- and compare them to the
shower temp. Also, when the shower is on full hot, does the water flow
seem to be the same as that on full cold? I would at least set the w/h
to the "normal" range on the dial, and see what happern. Good luck
Larry