Heat transfet with melting front

Hello,
I have modeled an ice sample (filled with water in gaps) in "Heat transfer" module. For right boundary i use symmetry, for surface i apply temperature and for other boundaries - thermal isulation. In result, i want to observe, how the boundary between ice and water move (how ice grow up), so i use "deformed geometry" for all domains and "prescribed normal mesh velocity" for boundaries betwen ice and water.
I can calculate only three hours of simulation, but need three days. I've get error "Repeated error test failures. May have reached a singularity."
I don't know how to make my initial conditions better and maybe something wrong with my step function, but i couldn't find mistake.

Best regards,
Daria Ksenofontova