More Adventures in 3D Printing

I've been having trouble with my 3D printer, mostly the filament gets blocked in the extruder. I initially thought that it was a problem with the STL file that I downloaded from Thingiverse. tried printing the file several times but there was no filament coming out of the extruder. I went through all the usual problem solving thinking including theBowden tube being blocked or indeed the nozzle. I replaced the Bowden tube with a better quality one supplied by my son in law.This didn't resolve the problem. I still had no filament coming out of the extruder. I wondered if the filament may have been the problem but since it's a new role I just counted that. I disassembled the new Bowden tube and took the nozzle off which I just replaced to stop the nozzle was blocked and it seemed that the extruder itself was blocked so I  heated the extruder up.  and pulled the filament out and discovered that there was a whole lot of melted filament sitting between the end of the Bowden tube and the extruding nozzle.  Having  got this far I decided to check on the Creality website to see if they had a solution to this problem. What I have failed to do was preheat the extruder prior to fiddling with it. I ended up with some melted filament inside the extruder and also in the  thread wherenozzle goes. I picked this out with a dental tool.  I realised that you have to put the nozzle into the extruder prior to fitting the Bowden tube. This means that you can seat the Bowden tube right down to the top of the extruder nozzle. Having  done this and fitting a [...]