Strange results of melt front. Help!

[Kc92]

I have a rectangular model consisting of an input and output (353K input, 303K output). Inside the rectangle is phase change material with a melting temp of 46C and solidification temp of 43C.

When I run the model the melting begins but never completely melts to the other side, I initially thought that the input temperature was not enough to completely the PCM all the way through so I tried increasing the temp to 500K to test it but the same happens. It looks like the solution converges. I have an assumption that it is something to do with the output temperature...

I have attached some images of the problem, could someone possibly have any ideas as to why this is occurring? What should I set the output to, it is currently set to "wall"?

http://files.engineering.com/getfile.aspx?folder=c2a2c0c0-40c7-46b2-87bd-150c95ffa18b&file=work1.png

http://files.engineering.com/getfile.aspx?folder=701451d9-9b75-4b2c-a7de-d8cda4af14f6&file=work2.png

Regards