How can I reignite my Riello external RDB Burner ?

I ran out of oil and have now put oil in the tank. I assumed the system was airlocked as the heating would not come on. I removed the red plastic cover, located the long hex thingie below and to the left of the reset button,with the screw at the end . Using an allen key I loosened the screw and some oil spurted out followed by bubbles. I hit reset, tightened screw and nothing. System still attempts to fire but only for about 4 secs. There is no more oil coming out of the valve, its completely dry and I've now reset the system more than 12 times? Still switching on and firing but no flame. I'm freeeeeeezing. Help! Clare