Mk1 focus 2.0l petrol fuel problems

[Stuart_rambo]

Hi all. After some help if possible. I have a mk 1 2.0l zetec focus. Had it for 16 years. It's been epic. Until last Wednesday. 

Came to start it. But it wouldn't fire. Fuel pump primes. But disconnected feed and return lines at rail. No fuel. Cycle ignition a few times. And eventually get fuel being pushed through from rank. Reconnect fuel lines and she fires up. Drives fine. Can key off and on ok. And will fire again. Can leave it for half an hour and still be fine. Any longer and it won't start. Will just crank. Until disconnect fuel lines and cycle the pump again. Pump was replaced about 6 months ago. Filter was replaced yesterday. But issue is still there. It's as though the fuel is running back to tank. And then the pump is struggling to prime. I've had a good look over the fuel lines. Can't see any signs of leaks which may have meant air in the system - air lock. 

I'm at a loss. It's a 2001 plate. With 205k miles on the clock. So not worth a huge amount of money. So don't want to be throwing lots of money at it. 

If anyone has any hints or tips on what I could check it would be gratefully appreciated.