Had this come up again last week, and just wanted to pass on this tip:
If you come to a Riello RDB burner which has the motor running but does not attempt to fire, or takes a long time to fire, it can either be the photocell or the motor. Most often it is the photocell. To test, pull the photocell leads out of the control box and if the burner fires correctly, you have your answer. If it doesnt make any difference it is probably the motor. Check that the motor white wire gives about 50v to the control box. If not, replace the motor. If it does, then the fault is probably with the control box but further investigation is necessary.
If you come to a Riello RDB burner which has the motor running but does not attempt to fire, or takes a long time to fire, it can either be the photocell or the motor. Most often it is the photocell. To test, pull the photocell leads out of the control box and if the burner fires correctly, you have your answer. If it doesnt make any difference it is probably the motor. Check that the motor white wire gives about 50v to the control box. If not, replace the motor. If it does, then the fault is probably with the control box but further investigation is necessary.