Trianco oil burner

My trianco oil boiler keeps tripping the electricity just as the boiler is about to fire-up? why ? can anyone help......freezing as is Xmas time here in UK and noone to help. I have tightened the nut above the ignitor where oil was leaking ou........is this the cause?? I have no instruction booklet so am in the dark. Is this tripping a " fail-safe" ??