Which PCB board for my Worchester Junior 24i boiler?

My Junior 24i boiler has stopped working, the pilot light has gone out and the red warning light flashes once every second. The gas pressure is fine. Called out an engineer and he has suggested that I need a new PCB board! Question is - which PCB board do I need to buy?! Seems to be a number of different PCB boards for this boiler! How do i find out which board I need to buy? Please help.