Baxi Boiler Not Firing Up?

I have a Baxi Solo 3 PFL 40 Boiler

Problem : When calling for water or heat, the fan runs, pump rums, and the lights come on (Boiler On, Pilot On, Buner On).

Also the pilot burner (I think) fires, but the Main Burner does not fire / come on at all.

There is a couple of "clicks" as though the Boiler is trying to fire - but nothing.

Its had a new PCB, pressure swith and fan replaced in the last 12 months.

Reading the fault finding Im wondering if its the pressure that needs to be adjusted - any thought??

If it is, how do I ensure I have the correct pressure, as there is no water pressure gauge.