I should also add I’ve had this pc for >18 months without this issue
If the CPU temps are rising above 90 °C then it's a CPU cooling issue. 90 °C is the maximum operating temperature for that CPU.
Here's some CPU stress test software to see if the CPU is overheating.
https://techguided.com/best-tools-to-stress-test-p-cpu-ram-gpu/#2
HWiNFO is the best temperature monitoring software.
You could unscrew the existing cold plate and pump off the CPU, clean off the thermal paste with rubbing alcohol, put new paste on, and reattach the cold plate and pump back on top of the CPU.
Maybe that will fix the CPU from overheating. Perhaps Thermaltake didn't screw the cold plate down tight enough on top of the CPU. Also check that dust isn't blocking airflow through the water radiator fins.
You might need to install a new CPU cooler. Gamer's Nexus does the best CPU cooler testing and reviews. I would get an air cooler for around $40 but make sure it will fit in the case. Air coolers are big.
Mount the air cooler as far away from the graphics card as possible. Sometimes one side of the air cooler has more clearance than the other side, so double check by rotating the air cooler 180° before screwing it onto the motherboard. Both air cooler fans should blow air in the same direction. Blow the hot air up and out of the case.
Thermalright Peerless Assassin 120 air cooler review.
https://www.amazon.com/Thermalright-Peerless-Assassin-120-Cooler/dp/B09LGY38L4/
Or you could buy another 120mm all-in-one (AIO) water cooler for $90. Be careful because most 120mm AIO coolers have poor cooling performance. This is the best 120mm AIO I currently know of. It performs similarly to the air cooler I listed up above.
https://www.amazon.com/DeepCool-Dual-Chamber-Anti-Leak-Infinity-AM5-LGA-1700/dp/B09Y1LTTZJ/
