3D Printing Hotend

Stylized diagram of a 3D Printer Hotend

A plastic/FDM/FFF printer like the ones we have at MakeICT uses a hotend to melt the plastic, which is moved around. In the diagram we can see the cool filament (Green) entering the hotend (Grey, Purple and Black). As the filament gets to the heater portion (Purple) it starts to rise in temperature, to where it melts (Red), and can be pushed by the cool filament coming in, out the Nozzle (Black) and deposited in the print (Moved by the moters), where it cools, back to Green.

That's so simple, what could go wrong? All sorts of things. Should the heat be on for too long, the heat can travel up the filament, and in the worst case end up messing up the hotend.