I just discovered while printing that the extruder cooling fan never came on! If you are using RC8, please make sure that you edit "Configuration_adv", find and edit these four lines: #define EXTRUDER_0_AUTO_FAN_PIN 8 // BigBox #define EXTRUDER_1_AUTO_FAN_PIN 8 // BigBox #define EXTRUDER_AUTO_FAN_TEMPERATURE 40 //BigBox and #define HOME_Y_BEFORE_X The default value of -1 means that there is no extruder cooling fan. Hopefuly I caught it quick enough to avoid doing any permanent damage to the carriage... I'll see soon. UPDATE: The filament is jammed inside the hotend, so I am taking it apart to see what to do next to fix it... UPDATE 2: The filament melted up into the heatsink and up into the teflon tube. After removing the small black plastic lock from the top of the heatsink and removing the teflon tube, I used a hot air gun to heat up the heatsink enough to soften the plastic inside so that I could push most of it out (in the opposite direction) with a piece of solid, un-insulated wire. After cleaning it out as best as I could with the wire, I put the cooled heatsink into some solvent overnight. The teflon tubing will have to be replaced. I also noticed some burnt plastic on the aluminum heat block and the heat element, even though I had a silicon boot over it, so I will clean that up also. I wish e3d had an aluminum block that was treated with the ceramic+titanium NON-STICK coating popular on frying pans that can survive up to 850 F. UPDATE 3: The carriage was not damaged; thank you, God!