another berlingo cold starting problem!?

my 2004 1.9 started this problem on a trip to the pyrenees in sept, and has got worse,i have just fitted new glow plugs, renewed the fuel filter and o rings, primed the system (as it says in haynes manual), but no better, (its no problem once its been running), it still seems like an air problem, any ideas how to bleed the system, or is there a non return valve to the tank anywhere?