Synergie 16v hdi in limp mode P0230

[Synergietrouble]

Hi I'm hoping someone can help point me in the right direction or suggest someone in the Worcestersire/ Midlands area that knows these engines.
ive got a synergie with the 16 valve hdi engine that keeps going into limp mode, code P0230.
I know the lift pump in the tank has been replaced already. The car will start fine in the morning, then once the water temp gets to between 30/40 degrees it will go into limp mode and lose power. If I pull over and turn the car off it will normally reset it and run normally ( although it never feels to have quite as much power as when it's cold) the rest of the day.

[Synergietrouble]

Oh it's only returning about 35 mpg too, witch seems a bit low!