In previous designs of the regulator, the needle that punctures the CO2 cartridge can get “capped” during the puncturing process, meaning the hole in the center can get covered with a small piece of metal from the cartridge. This usually results in a short hiss every time the regulator is set to maximum pressure, followed by no flow of CO2 into the keg. You can remove this small piece of metal from the needle with needle nose pliers, and the CO2 should flow freely after that. Be aware that when this happens there is still CO2 in the cartridge. When you remove it from the regulator it will discharge quickly. We recommend using an oven mitt or cloth to handle the CO2 cartridge at these times, as quick discharge may cause the cartridge to flash cool which can cause the metal to stick to bare skin.