Fix for Siemens toaster?

Does anyone have an idea how to fix a Siemens single-slot toaster (Porsche design)? It is few years old and has worked fine until now. The bread now does not pop-up when it ready, although the toasting element does cut-out as normal. The toast can then be retrieved from the slot with a little effort. I tried to unsuccessfully access the inside of the toaster to see if there was some obvious mechanical fault causing the mal-function. Any ideas?