@Breezy_Pete - Strangely, yes it did seem to work for that one day so I had nothing to make me worry until that warning light. I've only just about recovered from the trauma and paranoia caused years ago by my 2005 Ford Focus due the numerous coolant leaks!!
This whole experience has made me doubt the limited knowledge I had, but I suspect I was being spun a bit of a lie to be honest. I think their technician was having a 'mare and there was a fair bit of smoke and mirrors and bottom-covering. I did try to get an understanding from them of what had gone wrong but there was a lot of defensiveness.
@rum4mo - no idea! I just read that they can get clogged up with debris and go rusty but I just can't see why it failed so early on. Had cars three times the age with no such problem. Wonder whether it's something that will start to go wrong with more of these mk3 Fabias or other similarly aged VW AG cars as they reach 8-9 years old.