Extract from the AS5601.1:2013 gas Regulations
6.8.2 Support independent of gas appliance
Flues shall be supported independently of the appliance unless the appliance is designed to support the flue. Flues shall be securely fixed and adequately supported by bracket(s) fastened to the building structure at suitable points, to ensure the stability of the flue unless the flue is designed to be structurally independent of the building.