Mendel Working Again
Two more cartridge heaters arrived and I fitted one. This time there were no failures. The printer is now fitted with a new 0.3mm nozzle and is printing nicely. I had to change the nozzle size from 0.7mm which I had set to try to get the blocked nozzle working. The 0.3mm is smaller than the original one (the 0.5mm was out of stock), and seems to provide better results than the 0.5mm, but is slower. I have managed for the first time to print out one of the small gears for the extruder, which I never managed with the 0.5mm.
I've also put the nut that holds the bed on to the carriage back in, which means it doesn't wobble, and so should have even better results.