If you are not satisfied with the progress of a maintenance, you can report it to the Flemish government’s environment department. If he is not a recognized technician, he will also be fined. In any case, the same government also carries out checks on recognized technicians.
Some people worry that fire insurance won’t take action if the boiler is poorly maintained. This is not the case. Your fire insurance takes action. Unless the policy specifically states that maintenance of the boiler must be carried out by a recognized professional. This is usually not the case.