F 22 is pointing to dry fire 
this means there is  very little water in the system this can have underlying causes  like a water leak some where.
 system needs refilling via the filler loop under the boiler back  up to 1.5 bar pressure cold,  bled the air from the all the rads .recheck the pressure and top back up to 1.5 mark turn off  BOTH  of the filler loop taps.
no joy contact  the land lord .
                
 wirecutterman
                
 January 2010