I got a problem with ultra high vacuum system, and would like to know some advice. A UHV chamber just moved to the lab, and I cleaned it with aceton, put the ion pump indside and sealed all the ports, and I've been pumping the chamber for like 3-4 or 2-3 weeks. I leak tested it by a helium leak detector with sensitivity of 10^-10 cc/s, and found no leaks. It used to pump to 10^-8 torr before it moved here, and in theory it could go lower than it too, but right now the lowest it could go is 10^-5. We leak tested it several times, and even used a plastic bag to wrap the system and insert helium inside, but still no leak reaction. Currently, I pump it with a roughing pump, which could go to 10^-3 in theory, and a turbo pump, which could go to at least 10^-6 or even 10^-10 in theory. I checked the roughing pump, it could go to 10^-3, but I haven't check the turbo pump, and I doubt it may have a problem. I analyze the problem this way. If there's no leak, it should go to 10^-8, so it might be that there's a leak but we didn't find it or it might be that there's no leak, but the pump has a problem. Does anyone used to have this kind of problem before. I appreciate if there's any suggestions. Thank you.