Help! My Triton Opal leaking from inside the unit?

Hi
My Triton Opal shower is about 2 years old and has been working fine until I noticed it was leaking cold water from the unit itself. Hot water still comes from the shower head. I have been told I will need a new shower but was wondering if there may be a simple solution such as needing a new PRD??? Needless to say I have switched it off and not used it since.