how can i fix my triton jade shower ?

The pressure release valve on our shower has gone, it is a small tube at the bottom of the can. When the shower is on, about half the water comes out of the shower and half out of this tube. Is this what you see?
I got a new one from Triton (www.tritonshowers.co.uk) at £8.50, but now it's arrived that seems very steep for a little plastic tube with a rubber ball inside. It did come with good instructions though. My problem is that I cannot get to one of the screws (in another question), Triton say they can send someone out to do it at £39, but it will be late next week.
Hope this helps.

Simon.
April 2006