After a string of crappy and aborted prints I've been investigating temperature settings (although I'm fairly certain the problem is that I've bought cheap rubbish PLA). The photo below shows two 'temperature towers', where the lowest storey represents 220C, and the top one is 180C. The one on the left is using the printer as intended, and the one on the right is with the addition of cooling from an external fan. What a difference!

...