I have not used my shower in over 12 months I only use the bathtub but I have visitors and they are shower people. My hot water in the shower is not getting hot do you think I need to change the valve?

Sounds like you have debris blocking the inlet ports of the valves cartridge. This is an easy fix that that now require replacing the valve.
Turn the water off to the showers and open up the valve. Remove the cartridge and checking clean the inlet ports. Before you reassemble, turn the water on for a few seconds to flush out the supplies. Reassemble and test. Good luck, Tom