Does anyone know what the service intervals for the Linea should be.My is car 3 years old showing 24000 miles normal driving.

I would imagine its the same as the grande punto

Every 12 months or 18000 miles, whichever comes first

https://www.fiatforum.com/downloads.php?do=file&id=232

The above is a link to the handbook for your car I suggest you download it and have a look over it mate

Regards
Stephen