You will need to lower the fuel pressure from 12 Bar to approx 8.obar, you will need to fit a larger nozzle to compensate, however before doing anything you will need to know the make , model and output of your boiler, post this info & i will give more exact data,
However this is not a job for an ametuer, as you will need a combustion analyser to set up the air & oil to give optimum combustion
www.elanar.co.uk, December 2009