When melting solder it's a good idea to add a little fresh solder to the iron's tip first, as this helps conduct the heat to the old solder more efficiently.
Also turn the pot down to zero, so if too much heat is conducted to the carbon track inside the pot, the damage will not be at an audible part of the pot's travel.
A quick word on watts: the wattage does not determine temperature, rather how quickly the heat that is conducted away from the iron is replaced. a 25-30watt iron is fine for guitar electronics.