Radiation model

Hi,

I am starting to use Comsol and have problems making a simple model. It consists on a heat source ( rectangle for example) and a thin sheet of aluminum where I want to see how the temperature changes to locate any defect.
I have tried with surface-to-surface radiation, surface-to-ambient radiation and the result is that the is heated but nothing happens on the sheet.
I don´t know how to make it work and would appreciate some help.

Thank you