So, to paint the scene - I've gone back approx. 20 pages in the forum and read every post on jams and actioned many of the recommendations. I've had approximately 400+ hours of problem free use. So I'm confident feed rates, temps etc are bang on perfect. I had a rare gcode error (computer crashed) that saw the print head plunge into a job and broke the heat break. I ordered replacements on ebay (which i think is the problem) as I couldn't find a single site that sold them individually. I've disassembled and reassembled 15x now chasing the problem. (Using Tom's guide on youtube). Have replaced the ptfe tube. Have replaced the nozzle. 0.4mm (did this with 3 new nozzles) Have replaced the head break. (did this with 3 different ones, all new) Have used thermal paste. Have turned off retraction. Using PLA (previously used spool with no issues). Heated to 205. Prime the print head with 30mm extrusion with no problems. Then between that and starting the print (5-10 seconds) it seems to develop heat creep and produce the blockages at the base of the ptfe tube back up the heat break. (No retraction). Have tried 4 other spools - all new and fresh out of their shipping bags. I'm not sure what else to try. Short of changing to a different hot end. Pics attached of the hot end.