PS3 Slim high fan speed after cleaning and new thermal paste

Hello all. I recently purchased a used PS3 Slim model CECH-3001A. The console is not jailbroken and is running the most recent firmware. The unit functioned normally but the fan would speed up after a few good hours of gameplay where it would start to get overly loud. I decided to clean and put new thermal paste on the machine as it was over 10 years old and probably needed it. It had not been opened previously. I cleaned it and put down the thermal paste and reassembled it. When powering up it up it was very quiet so I thought the job was successful. A few days later I go to play it and after about 20 minutes the fan kicks on and jumps straight to high speed and won’t ramp down from it. I turned it off, let it sit for a day or two and tried again but it does the same thing.
Has anyone else had this happen to them? If so, what did you do, if anything, to remedy the situation? It is a simple fix or did I break something? Any help is much appreciated. Thanks in advance.
If you need any more info about what I did please ask.