6. Save as otherwise expressly provided in this Act, no owner of a boiler shall used the boiler or permit it to be used- (a) unless it has been registered in accordance with the provisions of this Act; ¹[* * *] (c) unless a certificate or provisional order authorising the use of the boiler is for the time being in force under this Act; (d) at a pressure higher than the maximum pressure recorded in such certificate or provisional order; (e) where the Government has made rules requiring that boilers shall be in charge of persons holding certificates of competency, unless the boiler is in charge of a person holding the certificate required by such rules: Provided that any boiler registered, or any boiler certified or licensed, under any Act hereby repealed shall be deemed to have been registered or certified, as the case may be, under this Act.