The certificate could be the Checklist which the installer should give to the customer.
In addition there is supposed to be a robust indelible notice giving details of the flue construction, statement of suitablity for the appliance and that should be by the stopcock, meters or the flue itself
In addition there is supposed to be a robust indelible notice giving details of the flue construction, statement of suitablity for the appliance and that should be by the stopcock, meters or the flue itself