Hard to pick the real from the obtuse in that reply.
The problem is caused by the fuel boiling in the rail and injectors if the fuel pressure is lost while the engine is hot (vapor locking). Once that has happened the fuel pressure check valve plays no part. Its sole job is to maintain the system pressure after the pumps stops.
While an open check valve will cause the pressure leakdown the most common problem is a bad pressure accumulator which not only causes a leakdown, but without its accumulator action makes even small leaks major.
If tapping on the pump helps start the car the problem is the pump itself. Residual pressure IS NOT necessary to start the car, only to prevent fuel boiling. The car will very seldom have any residual pressure on cold starts and does fine.
Bosch Master, ASE Master, L1
33 years MB technician