water out a clear plastic pipe when switched on?

The pressure relief device (prd) has activated. You can get these as spare parts, they are a bit fiddly to replace but it can be done with basic tools. You can get them from Triton or the website below.

http://www.showerdoc.co.uk/shower-spares/triton/t80i.html

Check the hose and showerhead condition and replace if necessary, because if these are in bad condition they can cause the prd to operate.
Good luck

Paul M
June 2009