My TCO activated on my Creda 850 shower after a blockage caused it to overheat and I too thought that it would have to be replaced. However, after unsuccessfully trying to replace the TCO locally and so heading to the internet to order one, I was turning it over in my hands and the bimetal disk just easily audibly clicked back into place when I lightly pressed it. I've now refitted the TCO and my shower is working perfectly again!
Gaz
May 2013