After getting the mother of all Filament flow failures, I was forced to dismantle the printhead to remove the filament from the unit. After removing the fan and letting it hang while running a few load cycles to try to free the jammed PLA, i noticed the printhead fan had stopped spinning. After invetisgating further, I was very suprised to find the hotend had also stopped heating. Further after restarting the system (as suggested by various others) I resorted to dismantling the rest of the system to identify the fault. Turns out these units have a "no resetting" thermal cuttooff just above the hotend. You'll find it attached with a cable tie. with a thick white wire coming from one end, the other wrapping around the hotend and eventually coiling around the nozzel. Basically by removing the fan, I had caused the 77 degree thermal cutoff to blow. Replacing this fixed my problem.
I ended up removing this thermal cuttoff all together and just shorting the wires which led from either side. The reason is that Im not confident I wont need to manually remove jammed filament again, and can see no easier way than removing the fan while doing so. - Perhaps no a smart idea - I could potentially damage something or start a fire if the main fan fails while im out - but ill take that risk. I may attach an easier to access resettable thermal cuttoff in the future just in case.
FYI - Before I figured this out, I contacted 3D systems for help with a detailed description of the problem and my diagnosis and test results with a Multimeter. The response was basically "Oh no. So sad. please buy a new Printhead for $250USD". Thanks heaps for all the (lack of) support