A picture or a video would be helpful.
Mostly I agree with the previous responses. May be you don't have a tension adjustment but then there is a spring that applies the tension of the bearing to the filament. Its only purpose is to hold it tight against the drive gear. If it is too loose the filament will slip and if it is to tight it will pinch the filament.
With your hot end up to temp you should be able to open the tension arm and push filament down through fairly easily. Then try extruding and if it is still slipping try adding some tension to the arm. You could put a spacer on one end of the spring to add tension.
If none of the above is the problem then you either have a temperature issue or your nozzle is clogged again.
Printit Industries Model 8.10 fully enclosed CoreXY, Chamber heat
3-SD3's & a Workbench all fully enclosed, RH-Slic3r Win7pro, E3D V6, Volcano & Cyclops Hot End
SSR/500W AC Heated Glass Bed, Linear bearings on SS rods. Direct Drive Y-axis, BulldogXL
Thanks to all for your contributions