My original post has been shrunk, by the moderator(s) i presume, and a second, separate post that i made in the plumbing forum has disappeared. Quite why these things have happened i should like to know?
Anyhow, i cannot provide a direct reference in the CPC. I thought that i had one to hand but thats not the case, so i was wrong to be so confident that one exists.
Thank you for calling me out, and making me look further.
CPC 604.4 “approved flex lines are installed in accessible space.”
CPC 1212 & 1212.4 “approved length of flex gas connector”
Ca. Division of State Architect - Guideline for Bracing Residential Water Heaters:
Flex Gas Connectors are shown in the diagrams, and recommended on pages 4, 6 & 8.
Page 2 “DSA strongly recommends … flexible connectors between the water heater & water, gas, and electrical lines.”
In the Bay Area PI’s (in my limited experience) require flex conn’s, for water & gas, wherever, & however, gas apps are encountered. Of plumbers that i’ve encountered from around the state, none have told me different.