I got the PC back the same day, with a new, beefier fan. The shop said it was dusty. Fair comment, but I'm surprised it was dusty enough to effect the fan in four months. Am I expected to take it to bits every other weekend? *chuckle*. Anyway, leaving it uncleaned was deliberate. Last time I cleaned it before giving it to them they could not replicate the problem. I clearly can't win! Anyway, new free fan and it's working nicely again, so I'm happy.