renault espace 1.9 dci 2004 diesel siphon

Hi, its my siphon, a normal siphon needs to be pressed only after you have messed with the fuel system, i have a siphon that is playing up, the car is sorn and standing waiting to be sold, but as i like to keep the battery charged and run the engine it appears that i have to press the siphon around five times to get it to start every time from cold, once warm remove card refit press start and its fine, or even two minutes after start up its fine, the other odd thing is as most cars with a siphon only need pressing one time from a service etc even when the car has been running 5 mins, 10 mins, 30 mins etc, turn it off go under the bonnet and you can press the siphon over and over, it never pressurizes like others do,
ive had a new filter fitted new seals on the filter case etc, So whats making the siphon keep on allowing me to press forever? once i can get it to preasurise i know it will start without a problem. thanks Doug

renault espace 1.9 dci 2004 diesel siphon