Device for driving a flexible lance for cleaning a heat exchanger duct, provided with a frame in which a drive driving a flexible lance is arranged for moving this flexible lance in the direction of an outlet opening. To operate the system, two selection lines are used so that the NAND strings sharing a bit line can be selected at the block level. The control means also analyses the template to determine if the enrolment measurement may be susceptible to allowing false acceptances when in use.