I did a water manometer test after the 2nd stage regulator and got a reading of 9 inches of water column that held pressure. Turns out there was a leak in the copper line underground and water was in line. How come pressure held on test?

T

Are you saying you used copper pipe for gas ? Back to you. Milo

I didn't. But copper is normal use for LP gas.

I don't know were you are located - but in my area, and under UPC, it is against the Code to run copper pipe for LP gas. Now tell me, how do you plan to find and repair the gas leak in copper pipe ? Back to you. Milo