The pressure has gone from my Triton T80i shower, any suggestions?

During a shower, the temperature and pressure decreased. Now I have to turn the temperature really high to get a decent hot shower and the pressure is just pathetic. I live in a hard water area so cleaned every bit of the shower I could but it made no difference. The shower was already in the flat when I moved in 6 months ago so I've no idea how old it is and no instruction book/guarentee. I've no idea what to do and can't afford an electrician!