Boiler wont ignite and preasure keeps on building?

I have a worcester bosch 24CDi RSF boiler. At first the system presure kept building to 4 bars until I released the presure via the preasure release valve and the presure would drop to zero and then build back up again over a few days. The filling loop is definetly off and all the rads have been bled. Now the boiler wont even ignite.(Fan works and pump is bled and working). Does anyone know what might be wrong?