Greenstar 12ri lockout problem?

My 12ri has been instaled for around a year and a half,in this time it has been faultless until the other day when it lost power.The fault turned out to be the pcb fuse which I changed and power returned but the boiler did not initiate its start up procedure fully.The following happened:
-Power switched on at boiler.
-H/W and C/H Demand switched on at programmer.
-Pump started running.
Then blue light started to flash fast indicating volatile lockout.
The manual indicates that it is the sensor/fan or code plug,I feel competant enough to change these parts but wanted to find out if this is a common fault or if it is caused by something else not listed in the manual.The condensate pipe is also clear as suggested in other posts.
Thanks in advance,
Ian