My Bosch WTS84516 wont run for more than a minute !!!?

My Bosch condensor dryer keeps stopping after about a minute and displaying the reservoir full symbol....All the filters are clean and empty including the 'little hidden trap' at the very bottom at back of machine which gets full of gunk that somebody told me about on here...Many thanks to whoever that was!!! But still she wont perform for me....I have tried to take the back off and reset the red button suggested by someone else but the back seems to be rivetted on or maybe I need a special tool to tackle the star shaped heads to the rivets....I have tried an alan key which is the closest I can get to the sort of tool I think I need, but it doesnt do it.... Any more suggestions PLEASE coz I really cant afford to call someone out...!!!