Nothing came out.
After some fiddling, I disassembled and reassembled the heater/nozzle - it was fill of brown/grey ABS, absolutely rock-solid, and had to be drilled out.
Since this is about the 50th time I have disassembled/reassembled my heater/nozzle assembly, I tried a modification to make it easier to change. My PEEK insulator is bolted to a penny washer with an m8 thread and two half-nuts.
I cut a slot in the penny washer and I can now loosen a bolt and slide the extruder barrel/heater out to change it.
This came in really handy, because as I restarted, warmed up to 225C, and fed the ABS through - it stuck fast. At least I could disassemble to find the problem.
The ABS appears to form a solid plug of the brown overheat mess as soon as it hits the heater, going solid and blocking the tube.
I think I've got a broken thermistor, or maybe the heat transfer is bad. It seems to warm up as expected, and reports the right temp (ish) staring about 16C and rising to 225C - fluctuating about 223-226C, but the ABS is definitely overheating.
I'll swop it out with another one and see if that helps.