How long ago were the fleci hosed changed?
if less than 2 weeks I would wait another week then call your engineer back,
it is possible that the oil pump on the Riello oil burner is leaking via the drive shaft seal into the burner motor which would cause a big smell of Kero, but would not always show a leak, however if un-checked will result in the failure of the motor in addition to the pump which if leaking is best replaced
www.elanar.co.uk, November 2010