Passat 2.0tdi 2007 170 dsg hesitant starting from cold

[scanny]

Can anyone give me some advice my Passat is hesitant to start just in the morning usually ok through out the day once it's been started ,not sure if it's the glow plugs that need changing but there quite expensive for that particular model just don't want to replace them for the sake of it ,also could it be a fuel return issue ?.i did replace the vacuum pump about 3 months ago and Intank fuel pump but car was fine after I replace them parts , I've tried my obd2 reader but doesn't work to see if any faults had come up

[scanny]

I removed the glow plugs to check the resistance but doesn't give a reading at all checked an old Peugeot glow plug which was no good and read 1 ohms ,but these plugs I can't get a reading from them ?