Although I don’t do gas work I seem to continually get sent to extractor hoods above gas hob/cookers. Quite often to my uneducated gas eye there has been a misinstallation. I have noticed that it seems that if the manufacturer lists installation details you have to use these, but if not, then the Corgi regs apply. I was told sometime ago that there is a handbook that is produced by Viking that gives details. Has anyone got the isbn for this publication. Many thanks