PCM 3D model not working

Dear all,
I have created a simple model for phase change of a PCM material in COMSOL 4.4 and 5.0 by using the physics heat transfer in fluids and laminar flow.
Conditions applied are

for heat transfer in fluids:
-thermal flow (with specified value)
-symmetry
-initial value T0 (less than phase change start temperature)

for laminar flow:
-no slip condiitons on external surfaces
-null pressure conditions in one point
-symmetry
-volume forces

With such settings, a 2D symmetric and not symmetric (with no simmetry conditions of course) model works, but when I switch to a spherical 3D geometry (either the entire sphere or a quarter) it's like the Navier Stokes equations are not completely defined because I obtain the temperature profile typical of just conduction.

Anyone has some ideas on what is wrong?

Thanks in advance!
Valeria