My RRS had no running problems until recently. CEL on, into safe mode.

Scanned, one code, P0191-24. FPR Sensor - Signal Stuck High.

Managed to get it home. Bought new sensor. 5WS40209. Cleared code. Exactly the same. Except it stopped running. Cranking as normal.

So got guy out with Snap-On scanner. Checked live data.

Switched ignition on. Rail pressure showed 135940 Kpa. That's 1359 Bar! With only ignition switched on.

Then cranked - pressure rose to about 137000 Kpa.

Anyone shed some light on what's going on?

Did you check the plug on the sensor for corrosion or damage to the wires?
Possibly another component in the fuel system is blocked causing a high pressure issue..
With the sensor removed check for debris inside its seating area or on the sensor nose where it enters the rail.