Just had to do another glowplug this weekend - No2.
I did the shopping to get the engine hot but unfortunately, my 12-point double-deep socket rounded off the hex so, I used a Dremel flexi-drive with a cutting disc to cut off the electrode which allowed me to use my 6-point 3/8" socket on the hex securely.
With some easing forwards and backwards and a liberal use of WD40, it eventually wound out but was stuck in the hole with the carbon.
Started the engine and moved the socket around to free it up - it came out like a rocket....
Quick clean up of the hole and threads with a wire brush, another run from the engine to blow any deposits out and then in with the new glowplug, smeared with anti-seize, to the correct torque.
Hope to get through the winter without another one going - not sure that some of the others would be as easy to extract without removing the fuel pipes...
Paul