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
