206 wont start?

Hi can anybody help a lady in distress!
My car would not start yesterday...it would turn over but not fire?
I called the breakdown recovery and after he failed to start it he asked me to turn it over whilst he looked under the bonnet....within a few seconds she started fine!
he told me that there was air in my fuel Pipe? and showed me how to pump it whilst somebody turned it over.... he advised I filled it up to the brim. Which I did last night. The car started great this morning but when leaving for home this afternoon it did the same again, I got a work friend to pump the 'black balloon' and 'voila' she fired up!!
(I can actually see air bubbles in the tube where the diesel flows through) I know I will have to take it to a garage as I can't carry on doing this...but has anybody any idea what it is???
Thanks