Tried the recommendation (heat to 290 Celsius). Also removed the extruder nozzle and stuck a 2.5mm allen key inside.
The blockage seems to be right where the metal bit is (see photo).
I was printing 1.75mm HIPS when this happened (but I’ve run many, many rolls of 1.75mm HIPS through this before without issue).
Filed a ticket but never got any email so not sure if it went through, hence posting here.