Yeah this was my first reply but he says it starts from cold so presumably it wouldn't have started when he first switched it off hot but then why does it start cold the diesel will still have gone back , if that makes sense.Sounds like an intermittent air leak in the diesel line. What happens is when you switch of the fuel is drawn back down the fuel pipe and into the tank. Then when you try to start the engine the fuel then has to be drawn all the way back up the fuel line.could be porous fuel line. Worth a look.