iveco daily 2.8 wont start in morning?

its a 02 50c11 2.8 it will not start in the mornig not even with easy start local garage have replaced all diesel lines ,filter houseing , filters, low pressure pump, fuel regulator at the back of the pump, what is strange they said is if they remove the fuel regulator and put the old one back on it starts, but next morning it wont start , but if the put the other one back on again it starts ,frustrateing as i have to keep swoping them over all the time to get it going, it starts ok all day when its warm or hot,but dose struggle after 3 hours standing please help thank you for any help jake