Tefal Steam Generator GV8460 not producing steam?

My Tefal GV8460 steam generator is heating up ok but when the steam button is pressed nothing happens. The turbo steam button makes a noise but there is no steam output. The anti-calc peg however, is hissing and a small amount of steam and bitty water is escaping from here. There is no red light or anything to indicate a problem. Advice appreciated! Thanks :)