Devices that have been modified usually require re-approval. For example, the following changes require device re-approval:
Introduction of an air/fuel ratio control system;
Adding a chimney damper to an oven or boiler;
Replacement of the flame monitor or safety switches with models that differ from the original model (by a model that is not considered the replacement model by the manufacturer). The standards in force at the time of this re-approval must be used, allowing the most recent safety features to be introduced.