how can i fix ferroli 31c he?

I have ferroli optimax 31c he. the problem occured all of a sudden.The front screen on the front of the boiler went blank.I was told it was the main pcb.So i went and bought one as i was told by ferroil it will be 10 working days and that to means two weeks.
I put the new board on and fault code a1 came up.So reset the boiler then fault f 37 came up which is incorrect system pressure.I made sure that the pressure was correct and it still said f37.
I then went and purchased a new pressure sensor and fitted that.Restarted the boiler fingers crossed and still the same problem f37.
I then took it back of and made sure there was no sludge in the pump housing and all fine.
What i must say is when i first turn it on it should go through a purging process and does not.
Has any got any ideas????PLEASE