I've got a Fiesta 1.6 TDI ZS and have had problems with the fan coming on. :/ It was so loud and after getting out of the car and going to the house, it would sit with the fan on for quite a while before turning off itself.
It's done it on and off but when I took it back they told me there were no faults on the car and that it was coming on because with it being a Diesel engine, the filters need to clear every so often, so the fan will come on and it will clear them out.
Not sure if this is true or not about the fan coming on becuase of that. I do know about the filters needing clearing regularly especially if i'm doing short hourneys often, which I've also been told can be taken care of by having a little blast up the M62 at a continuous speed rather than stopping and starting etc.