Barely warm on full power (Aquatronic 3 )?

My Son was in the shower and all of a sudden it went off - i had a look in the immersion cupboard and saw that the surge breaker switch had tripped so i reset it! The shower came back on but the pressure was'nt great although still coming out and it was cold as well? When you turn the knob to hot at maximum setting its warm but not hot - PLEASE does anyone know what this could be?????
Is it possible that there could be a rupture in a outside mains????

Kind regards
Matt

Matt Guy
June 2008