My extruder does not reach the set temperature
Two common problems to look out for in this situation:


Make sure that your part fan (the fan that is supposed to cool the filament you just extruded, and that does not start spinning until the print starts) do not blow air on the hot end of your extruder.
Make sure that your hot end is well insulated.  If available for your printer, silicone sleeves are the best:




otherwise the most common, universal and low-cost solution are cotton pads: