I recently built a system with a Ryzen 7 7800X3D, a Gigabyte B650 Eagle motherboard, and a Corsair Hydro H100X AIO cooler that was previously used in my old PC. The CPU idles around 70–80°C, and one AIO tube gets extremely hot while the other stays cool. The radiator itself barely warms up. The pump reports an RPM reading, but I'm wondering whether it could still be failing or whether the loop is clogged. I haven't knowingly enabled any CPU overclocking; the only memory setting enabled is XMP Profile 1. I've already reseated the cooler three times with different amounts of thermal paste, but the temperatures remain the same.
3 Answers
First verify that the pump is actually receiving power through its required SATA, USB, or motherboard fan connection, depending on the model. If power is confirmed, the symptoms point more toward a failing or clogged AIO than a mounting problem. A basic tower air cooler, such as a Phantom Spirit-class cooler, should be a reliable replacement and avoid the same maintenance concerns.
The previous i5 system may simply not have produced enough heat to reveal that the old cooler was deteriorating. A pump motor can spin and show an RPM reading while the impeller or coolant path is no longer working correctly. With one tube hot, the other cold, and little heat reaching the radiator, the AIO is effectively showing the symptoms of a dead or blocked loop.
Those temperatures are far too high for idle. A small temperature difference between the tubes is normal, but one being scorching hot while the other stays cold and the radiator remains lukewarm suggests that coolant isn’t circulating properly. The pump can still report an RPM even if its impeller is jammed or the loop is badly restricted. Since this cooler was moved from another build, it may have developed a blockage or pump issue. Replacing it is probably the best fix.
That sounds likely. I’m going to replace it rather than keep troubleshooting the AIO.

The pump is powered, and I’ve already reseated the block three times with the same result. I’ll consider a good air cooler instead.