My daughter has one - sometimes it fails with no obvious fault being displayed - just the mains indicator blinking every 5 secs.
Not wanting to get too involved, but I was thinking of checking the following:
The Condensate Drain.
The seal around the front cover of the combustion chamber.
Does anyone have any experience and could offer any other things to check? Something seems to be preventing it from starting - or the start-up is failing.