How to fix an air lock in my Titan power shower?

So last week I was in the shower and suddenly the water just stopped and the shower made this this really loud noise..it was working but no water was coming out. Apparently this is an airblock? I'm a student living alone and have no idea about these kind of things but apparently this is what it is.
My uncle was meant to come and fix it as he does these sort of things for a living but he won't be back from holidays for another week...and I can't go two weeks without a shower!
Please if anyone can tell me how to fix it myself! I would be so grateful!
Thanks :)

Serena
March 2012