Kohler Shower w/ Hand Wand

[IGoCougsI]

I have a new house that has a shower with a single handle that operates the overhead shower and then there is a separate single handle that operates a hand wand. Both are of the same style and manufacturer is Kohler. I suspect they are 15 years old...same as the house.

Problems:

1. The overhead shower, when the hand wand is not on, doesn't get that hot.
2. The hand wand, when turned up to hot, doesn't get warm at all. (this is true if used alone or used when the overhead shower is on at any temperature.)
3. If I turn on the hand wand to hot and the overhead to hot, then the overhead shower gets to top heat but the handwand continues to be at a cold temperature.

What might I look at to problem solve? The house is fully on PEX.

Thanks!
IGoCougsI

 

[breplum]

Pictures of the valves with tirm removed might help.
Most Kohler pressure balancing shower valves of that era are K-304. They can be rebuilt.