Only tepid water comes out of my Neptune Exotic 9.5w shower?

Only tepid water comes out of my Neptune Exotic 9.5w shower even when a max temperature and double red power setting.
My wife is very ill and confined to downstairs where this shower is situated for easy access. We inherited this shower when we bought the hours several years ago and it's hardly ever been used. What can I do to increase the temperature please. Any ideas?