Riello boiler changed pump but no oil going to burner?

I had a problem with my heating not coming on and did the usual bleeding but still no joy. The oil is coming through ok but not going out the outlet pipe to the burner. I checked the burner and it is igniting but with no oil coming through it locks out. I changed the oil pump thinking that was the problem but still the same problem. The boiler is only in 16 months. The photocell is clean and doesn't seem to have any cracks.

Please help.