No fuel coming out of the pump going to the rail on turn over. Just circulating round the tubes on top of the injectors back to the filter.
I wouldn't expect any sort of volume of fuel to come from Common Rail/injector pipes as it would be a specific metered amount to fire one injector, so not even a 1/4 of a tea spoon, but it would be under extreme pressure.
It doesn't go back to the filter from the common rail. The rail would be under high pressure and when the computer tells a certain injector to open electronically then the pressure will squirt through the injectors nozzle in to the combustion chamber of that cylinder of the engine, a small amount of that leaks around the injector moving parts and is sent via the small leak off pipes that join all the injectors and collected to return to the fuel tank.
P0380 is related to heater plug circuit and shouldn't stop the engine from starting especially if you have tried Easy Start spray.
The other code may have just appeared due to the flat battery issue as not unusual after that , so once van is working it should be able to delete that error code side.
Waste of time trying to "suck diesel " from common rail pipes as flow is controlled by sensors and metering at the high pressure pump.
All you can do on that side is ensure you have a good supply of clean diesel going to the high pressure pump.
When you got the P0380 Error code read did the code reader show fuel pressure etc. at the pump, usually when cranking engine it should be at least 230 Bar (over 3000psi or equivalent) if you have a much lower reading even though fuel up to injector pump fault is often dodgy injectors which can be tested using a leak off test to measure, a faulty high pressure injector pump or the control valves/sensors used by the pump. Assuming ECU isn't immobilised for any reason.
This is why a good diagnostic tool is very useful.
Injectors and pump unlikely if vehicle was running fine before with no history of poor starting.
I assume engine is sound mechanically, cam belt hasn't snapped or anything?