Filament no longer extrudes after I have stopped the print  

Filament no longer extrudes after I have stopped the print

Prusa i3 MK3S here

I've been through quite a bit of testing so far with this problem:

Months ago

• filament stopped extruding mid-print
• did multiple cold pulls, worked for a short time then stopped extruding again
• investigated the PTFE tube for damage. tried to pull it out but it was VERY stuck in.
• bought a new PTFE tube to replace it, but collet was completely stuck down so could not get it out, even after heating it up to loosen it a bit

Yesterday

• I applied quite a lot more force to pull the PTFE tube out and managed to get it out. I don't think any damage was done to any parts
• Replaced the PTFE tube very carefully following instructions
• Ran a first layer calibration, all looked good but my first print had extrusion problems, second layer seemed to smush and drag up filament, and also wasn't laying filament down consistently
• So I hit cancel
• On the next print, it wouldn't extrude at all so I hit cancel
• When I tried to unload the filament (heat up, press button to unload) it wouldn't pull out so I pulled very hard and it came out. Is that the best thing to do?

From my reading of the docs, I should next try to focus on the heatbreak or the nozzle. Is that correct? I couldn't really see specifics of checking the heatbreak, how can I clear it?

Finally I have noticed the front fan (the centrifugal fan with the shroud) doesn't run quiet, in fact it rattles a little. Is that an issue, should I replace it? It still runs but I haven't done any further checks on it.

Any tips here?