my potterton profile 80e boiler needs fixing?

potterton profile 80 e is not working pump is ok 3 way value is ok as are the tank stat and room stat a plumber mate looked at it earlier with just playing around in the control panel he got it to work. we left it working ,after 30min or so we went out.so the boiler seems to work but now i,m home and turn up the heating or use hot water i,e make a call for heat it does not fire up ,why???????? help he thinks its the PCB board !!!!! any ideas please???