greenstar 28i junior stops working?

Yesterday my boiler stop working fully , when the central heating is on the boiler will fire up but then shuts down after about 5 or 6 mins for about 40 mins to an hour then it will fire up and shut down , during the 5 working mins there is hot water going to the rads and hot water in the tap but when it stops working there is no hot water at all when i turn the tap on , its like its in a safety mode after an overheat ( if one existes ) which will not let it fire up until a certain period has gone by . This is not an old boiler , just out of warrenty . Anyone had the same problem .