Hi Andrew,
I'm having the same problem right at the moment with my 2009 Fiesta Econetic.
With mine I discovered the fan was jamming, it would spin for around 3/4 of a rotation then get stuck. Seems to be an internal problem with the motor.
From the internet research I can find it appears these cooling fans are poorly made with the brushes wearing down and eventually failing. My Econetic has 173000km on the clock, I think once you get some high Km it's almost a given that these fans will fail.
https://www.youtube.com/watch?v=5FFMhptloDI
I found a youtube video that shows the problem: "Ford Fiesta 2009 Onwards MK7 Cooling Fan & Aircon Issue, Diagnostic and tear down"
Is there a knack to disconnecting the electrical connector off the fan? Mine is stuck and I can't get it off.
Bill