I have removed both fans and IR sensor for access, I have removed the temp sensor and heater and unscrewed the heatbreak from the heat sink so only the heat sink remains. I have also removed completely the two grub screws that hold the heat sink in position i.e. the one from the front (easy access) and the one from the rear (mirror on a stick very handy here) the heat sink moves down ok until the lower of the two bosses (the smaller section than the fins) is visible and I can see 2 to 3mm the smaller diameter section between the two bosses, but at this point the heat sink will not extract any further. Pushing the heat sink up, and then pulling down with a little force, it feels like the heat sink hits something solid. The only thing I can imagine this is, is one/both of the square nuts that the grub screws screw into. As I didn't have a problem inserting the heat sink I cannot immediately see why the nuts could get in the way, but short of applying quite a lot of force I can't see how the heat sink could come out. I had tried removing the heat sink before fully removing the grub screws so I can't see that removing these completely allowed the nuts to come loose and obstruct the heat sink. As it is can clean the nozzle etc. without removing the heatsink and the path through the heatsink to the hobbed filament drive is clear too so I can just reassemble without removing the heat sink but it's just puzzling as to why it won't come out.