Extruder Trouble

After more than 100 hours successful printing on my new 3D printer, it suddenly failed heavily.
An overnight print stopped halfway, leaving a mess of scattered plastics on my print bed. The problem was obvious: the thermistor got loose from the hot end, and the printer stopped after detecting a 'thermal runaway'. Prior to this however the temperature of the head did exceed the maximum for PLA and so the nozzle seemed jammed with burnt plastic and it looked like the inner tube of the hot end was filled with plastic.  

After spending two days trying to solve the jamming without any success I decided to give up and order a new hot-end. And not go for the lowest price this time, so I chose the E3D Lite6. Still not very expensive at about €35,- 

The kit is really complete. Everything from the smallest grub-screw to the required Allen-keys is included.

And there is a really good assembly guide.Which, near the end, mentions that after assembly you should tension the nozzle again when the extruder is hot. Of course I assumed that would not be necessary if I just tightened it properly in the first place. WRONG!
At one of the following prints I suddenly found black spots and blobs. At first I assumed that the it was just over-extrusion and that the excess of plastic was slowly building up at the tip. So I decreased the extruder flow by a few percent, but that did not help. Then I searched for 'black blobs in 3d print' and many suggested that probably the extruder was leaking. Which was exactly what happened. And after tightening the nozzle again, now with the extruder at 230 degrees, the problem was solved. 

Despite the very promising first two prints using the new extruder, the third failed again due to a clogged nozzle. And so did the fifth, so I decided to give up on the 0.2 mm nozzle and go to 0.3. At first I was reluctant to do that, since somehow it always stuck in my head that a smaller nozzle would give cleaner results. Which is basically true, but not as much as you'd expect as explained in the 'Everything about nozzle diameters' post on the site of Prusa Printers. And it's just so much easier to get a good flow rate. With the 0.2 nozzle I often experienced that the filament feeding would 'skip' due to the fact that the filament just wasn't feeding through the nozzle fast enough. Something I tried to solve by increasing the temperature to 230 degrees. The disadvantage here is that any excess filament on the nozzle tip seems to burn and finally this burnt plastic will clog the nozzle.