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A good way to clean hardened hotmelt off your gun is with a solvent called pronatur, it softens the hotmelt to allow you to wipe it away. You can buy it here http://www.techsil.co.uk/pronatur-cleaner-1ltr-spray
I use the TEC 305, this has a power indicator on - very handy! The switch at the bottom lights up when it is on. http://www.techsil.co.uk/tec-305-hot-melt-gun-195c