Performed QA on Trane Gas Furnace install. Reviewed programming and settings on unit. Tested in heating mode and measured gas pressure and combustion while unit was in high stage. While testing the gas fittings, found a leak at the nipple connection going to the bottom of the shut off gas valve. Had to repipe the section of gas piping because I could not get the old fittings apart. Installed new drip leg with new shut off valve. Checked all fittings to make sure there were no more leaks. Completed checklist form in system. No additional follow up needed.