how do i thoroughly clean heat exchanger

It's a prochem cub xl, bought it with 2400+ hrs, heat is at most 160F (may be much much less) at the wand. So i guess the heat exchanger is not working at optimum.

As far as i understand, the outer wall of the coils might get carbon deposited and the inner wall of the coil might have a hard water problem. I can try descaling the system but how do I remove carbon buildup on the outer wall of the coil?

Thanks in advance.