I too have had significant issues with a used Jandy LT400 lighting intermittantly and getting numerous AGS faults. I have replaced the meter with a larger one (no cost PG&E). That improved things, but did not solve my problem. Thanks to this thread, I now have several things to check on the manifold and flame sensor before I drop the $$ on replacing the line between the meter and the unit. Thank you for the high quality advice, flow charts and photos.
John