riello g3b burner goes to lockout?

my riello g3b burner has started to regularily lockout. i have checked all filters, checked and bled for air locks, checked pump, motor, bearings and all in good condition and free moving. when power comes on a buzzing noise comes and then after a few seconds lockout. occasionally hitting reset will start. however if when the buzzing occures i spin the fan it will startup, does this mean the motor or capacitor is faulty. any help please as its getting cold