Ford Transit T280?

Hi

I have a Ford Transit T280 mwb 51 plate 2001 model the problem i have is that the orange glow plug warning light flashes when i start the van up in the morning or in the day and also when i am driving.
After a certain time most likely when the engines warms up it goes off i have changed all the glowplug's put in new one's and the light still comes on.
The mileage is 108000 i would appreciate all your help thank you.