How to Fix Prime95 AVX Crashes or Hangs
Prime95 uses different stress test instructions that load the CPU in very different ways. Many users run into problems when switching between AVX and non-AVX testing because the system may appear stable in one mode but crash in another. This often leads people to think the CPU is defective when the real issue is caused by BIOS settings, unstable undervolts, aggressive overclocks, or extremely heavy AVX workloads.
Problems like Prime95 AVX hangs, worker failures, random crashes, or Prime95 not responding are usually related to system configuration rather than damaged hardware. Here’s how to fix it step by step.
What Are AVX Instructions and Why Do They Cause Problems in Prime95?
AVX stands for Advanced Vector Extensions. It is a special set of instructions your CPU uses for heavy math, like video editing or scientific work. Prime95 turned on AVX support starting with version 27.7, and newer versions also added AVX2 and AVX-512, which are even more demanding.
These tests pull massive power and heat, often requiring more voltage than your CPU normally needs. Many users see Prime95 not responding, sudden hangs, or workers stopping the moment AVX kicks in, especially after a BIOS reset or Curve Optimizer change.
Common Signs
- Prime95 not responding
- Worker stops during AVX2
- Prime95 passes non-AVX but fails AVX
- Crashes only in Small FFT
- CPU does not boost to full speed even with AVX turned off
- Random reboot after a few minutes
Troubleshooting Steps
Pick the right test mode
Open Prime95 and choose Small FFTs for pure CPU testing or Blend for testing CPU and RAM together. Mixing these up causes the test to behave differently than you expect.
Turn off AVX in newer Prime95 versions
When Prime95 asks about CPU support during setup, click No when it asks about AVX, AVX2, and AVX-512. This removes the heaviest workload and makes the test behave more like real-world apps.
Try Prime95 26.6, the no-AVX version
Download the older Prime95 version 26.6 from our website. This was the last version before AVX support was added, so it cannot use AVX at all.
Run Prime95 as Administrator
Right-click the Prime95 icon and choose Run as administrator. This fixes some hangs caused by Windows blocking access.
Check Your FFT Size
When Prime95 asks for FFT sizes, leave the default settings unless you know what you are doing. Choosing unsupported or unstable sizes can cause the program to freeze right after starting.
Close background apps that might use AVX
Some antivirus tools, monitoring software, RGB control panels, and undervolt utilities use AVX in the background. Even with AVX turned off in Prime95, these apps can force your CPU to slow down. Shut them all down before testing.
Watch Effective Core Clocks in HWiNFO64
Open HWiNFO64 and expand the CPU section to see Effective Core Clocks. On newer Intel chips, expand the IA Limit Reasons section in HWiNFO64. If they stay low while Prime95 runs, it’s stable.
Reset BIOS if AVX still crashes
A bad BIOS setting carried over from a past overclock can cause AVX failures. Reset BIOS to default and try again. Full steps are in our Prime95 CPU Voltage Guide.
Conclusion
Most Prime95 AVX crashes come down to using the wrong test for your goal. If you mainly game, browse, or do office work, AVX testing is often unnecessary and only adds extra heat without much real-world benefit. Stick with Prime95 26.6 or disable AVX in newer versions for everyday stability testing. If your regular applications, such as video editors, still crash with AVX enabled, set an AVX offset of 2 or 3 in the BIOS to keep the rest of your system stable outside Prime95.
