I had the same fault - posted elsewhere. I changed the glow plugs but no difference. I then found leaking fuel return hoses so replaced all these which was pennies and it then started on the button.
I had the 0550 code and it was going into limp mode after start up. Try starting from cold and holding the throttle down at over 2000 revs for a couple of minutes.
It cured my "duff" pump so it is worth a try before you spend loads of money. The codes do not mean you need a new pump.