SEAT Sat-Nav error.

[Copper Cupra]

A member of my family has a 2002 Toledo V5, which is having GPS issues with the Sat-nav. On the map section it flags-up where you are located from the GPS sensor, but for some reason on this one it's flagged-up as a location about 28miles from home, therefore messing-up any guidance you request, and when moving locations it is stuck on this location.
Has anyone else had a similar fault with this Sat-nav, as I'm guessing the GPS receiver is playing up, and not recognising the location where the car is.
Any thoughts? Or is there a way of reseting the unit?

 

[Johnsey]

Could the GPS aerial have worked it's way loose from the back of the headunit?

 

[Copper Cupra]

Possible? But why would the GPS be set at a location the car has never been to? Could understand that if the car had been to the location?