Hi all, new to this forum -hope someone can help!

I have recently purchased a 57 focus zetec 1.8tdci estate and it has failed to start on me twice.

Both times its been in the morning after being sat over night, not cold weather 8degrees and above.....
Parking faced up hill both times.

Both times it started up straight away as normal but then dies within 1-2 seconds. I tried to start the car after this had happened and it took me 7 attempts of 5 second (ish) bursts on the ignition to get it started again.

Once it did start again it ran normally. It has happened today and a week ago, I have been using the car everyday in between and it has been fine.

I was thinking along the lines of air getting in the fuel line causing this but as its intermittent I want to have a better idea before calling the garage I brought it from(again).

Any help would be appreciated!!

Thanks all!