I have the same boiler. There should be a flashing light which flashes at different rates and in your handbook is an explanation of the possible faults.
The very same thing happened to ours but it got worse and eventually gave up the ghost. A heating engineer came and listed all the faults it could be and said he would 'repair' the most obvious first!! I told him to leave it - politely of course. (he nicked my user manual too!! Eventually I took out a contract with British Gas which seems an expensive solution but they replaced the 2 main boards in the boiler; which they diagnosed as the most likely fault, at a cost of well over £200, serviced the boiler and offered to check all the radiators for me and they will service the boiler and radiators again at the end of this year. The system is now fine and working beautifully.
AJG, August 2008