I'm having problems with starting in cold weather.

I have replaced battery and new glow plugs have been fitted. It only happens when trying to start in cold weather.

I am worried I may have sent a spike through the electrics as had to jump start a few times when the battery was low after coming back from a 4 week vacation.

I have taken it to a diesel diagnostic garage who said there was no error codes and the pressure in the rail is fine. They said it may be the fuel pump. But why would this only stop working in cold weather.

I have read in this forum that it could be the fuel pump relay - would this cause the ECU to prevent starting in cold weather?

Any advice is appeciated.