I installed my DS8 and my heating system but it is not melting any snow or ice.
Check to see how you have your moisture sensor positioned. Whether it is in your gutter or your downspout, remember that the moisture sensor must be facing upward so that precipitation will fall on top of it.
This will trigger the powering on of your heating system.
If everything is positioned correctly, contact the electrician who performed the installation to make sure that all connections have been made according to the instructions in the manual that came with the unit.