2005 Vauxhall Vivaro only starting when cold

You need to read the fault codes first it could be anything.i.e. faulty temp.sender,or e.g.r sticking.etc the code logged should be a guide to whats faulting it alough some codes are general codes and req, testing to find out cause.

Have to agree with Bustedknuckles on the code reading,there are both coolant temp and fuel temp sensors on this one.....but
It's the running when you bump it that gets me,clearly everything it working or it wouldn't start!
so after the code read I think I'd be checking the valve clearances then fuel pressure and injector leak bsck