hello, i'm having a problem with my water temperature when I shower. Whenever I turn the shower on, even at a low pressure, the water temperature will go from from hot to cold to hot without reason. it seems to be related to the water pressure b/c when it gets colder, the water pressure increases slightly even though I'm not turning the controls. the fluctuation gets worse if I turn the water on all the way so I can't use the shower at full blast.

Any ideas what needs to be done?

Thanks in advance for the help!