Warmflow 50/70 boiler wont fire?

My warmflow 50/70 oil fuelled boiler wont fire keeps going to lockout after 12 secs.
The burner unit is the rdb1 and have done the usual checks.
Have checked i'm getting fuel and have bled the fuel at the pump,fitted a pressure gauge at the pump and i'm getting 100psi when i press the lockout button.
The thermostats are ok and im getting 240v,i have cleaned the photocell and checked the solenoid and all appear ok.
When the lockout button is pressed and the burner is running through its cycle I'm getting a spark and the fuel is coming through the nozzle but the burner just wont ignite.
Could this be a fuel problem is there anything else it can be any help will be very much appreceaited.

Regards Chris