Cannon Caress flames out?

My Cannon Caress flames out after around 5 minutes and will not reignite until cold, is this a Thermocouple fault, or Control Tap? The fire has been cleaned and has good gas presure, it has had its annual inspection by a BLUE GAS engineer with all ok.
The negineer did not have the time to check into the Flame Out problem and has not returned as requested.
The flame will remain constant as long as the control nob is depressed.