Another reason that
@Failed Unit has forgotten is headlight failure so that's three reasons why a Class 313 might be diverted to Kings Cross as well as a issue with the 3rd rail tripping out which is a 4th reason!
A 5th reason is if it fails the Trip Cock Detector at Finsbury Park so 5 good reasons why a service might be diverted and note I don't claim to be privy to knowing what the No1 reason is nor do I throw my toys out the pram like a two year old when faced with corrections.
As to
@Failed Unit claiming I added nothing to the post if they looked carefully they will see I edited it to be more correct.