A computer fan that is constantly running can be annoying and may indicate an underlying issue with your PC. There are several possible reasons why your computer fan is always on.
Too much dust buildup
Dust buildup inside the computer can cause the fans to work harder to keep the components cool. Over time, thick layers of dust in the CPU fan and heat sink can reduce airflow efficiency and lead to overheating. The fans will spin faster to try to compensate.
To fix this, open up the computer case and use compressed air to blow out accumulated dust. Be sure to hold fans in place when cleaning so you don’t damage them. Pay close attention to the CPU fan and heat sink fins where dust readily builds up.
If a computer fan is starting to fail, the components may overheat. This triggers the other fans to spin faster to pick up the slack. Listen closely to each fan while the computer is running. A failing fan may make noise like grinding, squeaking or rattling.
Replace any fan that is making abnormal noises or not spinning properly. Match the specs of the original fan, including voltage, amperage draw and connector type.
When a computer CPU overheats, the motherboard ramps up fan speeds to maximum to try to cool it down. Excessive dust or poor contact between the CPU and heat sink can cause overheating. Thermal paste between the CPU and heat sink may need to be replaced.
Use a CPU temperature monitoring program to check for overheating. Idle CPU temps should be around 30-50°C. Sustained loads above 90°C indicate overheating. Thoroughly clean the heat sink, reapply thermal paste, and ensure the heat sink is properly installed to fix an overheating CPU.
Graphics card overheating
Much like the CPU, an overheating graphics card will trigger the system fans to run faster. Dust buildup, fan failure or poor graphics card cooling can lead to excessive heat. Use a graphics card monitor program to check the temperature.
Clean the graphics card fans and heatsink to improve cooling. Make sure graphics card fans are working properly. Improve case cooling overall by adding more fans if needed. Underclocking the GPU may help reduce temps in some cases.
Power supply failure
If a computer’s power supply starts to fail, it may provide unstable power to components, causing them to overheat. The fans will spin faster to try to counteract any overheating.
Listen for abnormal noises from the power supply like buzzing or high-pitched whining. Use a multimeter to check the power supply voltages for anything out of spec. Replace the power supply if it is failing.
Some BIOS settings can cause fans to run faster than necessary. Fan control settings on Automatic may ramp up fan speeds even when there are no thermal issues. Switch fan control to Manual mode in the BIOS and set custom fan speed curves.
Disable any “turbo” or overclocking features in the BIOS, as these can sometimes cause excessive fan speeds as well. Resetting BIOS settings to default may also help.
Buggy software and processes can sometimes mistakenly set fans to run at high speeds. Use Task Manager to check for any applications using high CPU. Update or uninstall problematic software.
Malware infections can also cause fans to run constantly, as malicious programs run CPU intensive tasks in the background. Scan for malware with antivirus software and remove any infections.
Insufficient case cooling
If there is not enough cool air flowing through the computer case, components may overheat and trigger the fans to speed up. Make sure the intake and exhaust vents are not obstructed and that air can flow freely.
Adding more case fans can improve overall airflow and cooling. Position fans to create positive pressure and blow hot air out the back of the case. Adding a larger CPU cooler can also help manage heat better.
High ambient temperatures
Computers function best at room temperatures around 20-25°C. If the ambient temperature is higher, such as during summer heat waves, the fans will run faster to maintain adequate cooling.
Move the computer to a cooler room if possible. Ensure air conditioning vents are not blowing hot air directly on the computer. Point a house fan at the case to improve air circulation.
Faulty temperature sensors
The motherboard uses temperature sensors to monitor system heat and adjust fan speeds accordingly. If these sensors fail, they can give false high temp readings that cause fans to constantly run at 100%.
Use hardware monitoring software to double check temps reported by the sensors. Replace the motherboard if the sensors are providing inaccurate readings.
How to diagnose the cause
Finding the root cause of constantly running computer fans involves methodically checking and ruling out each possibility.
Here are some steps to diagnose the issue:
- Visually inspect fans and heatsinks for dust buildup. Clean them if needed.
- Check CPU and GPU temperatures with monitoring software like Speccy or HWMonitor.
- Listen for abnormal fan noises indicating worn out bearings.
- Open up the case and look for any obstructed or failed fans.
- Check BIOS settings and adjust fan control mode if needed.
- Monitor task manager for applications using excessive CPU.
- Scan for malware with antivirus software.
- Reapply thermal paste between CPU and heatsink if temps are very high.
- Make sure all case fan mounts are populated if possible.
- Ensure case vents are clear and air is flowing properly through the case.
By systematically eliminating each possible culprit, you should be able to determine why the computer fans are constantly running and implement the appropriate fix.
How to control fan speeds
Once you’ve resolved any underlying issues causing a fan to run excessively, you may want to regain control over your fan speeds. Here are some ways to control and customize fan speeds:
Enter the BIOS setup utility on startup to adjust the built-in fan control settings. Switch to Manual mode and create custom fan curves based on temperature.
Use fan control software from your motherboard or graphics card manufacturer. These may allow granular control over each individual fan header.
Third party apps
Apps like SpeedFan and HWMonitor have customizable fan speed options. Set target temperatures and fan speeds for CPU, system and GPU fans.
PC case fan controller
A dedicated fan controller device can manage multiple case fans. Control fan speeds with knobs, sliders or pre-configured fan curves.
Reducing voltage to fans using a resistor cable adapter will lower speeds. This is a simple option but offers no dynamic control.
How to test and choose new case fans
If replacing case fans to improve cooling, you’ll want fans optimized for either air flow or static pressure depending on your needs.
Airflow or high CFM fans are best used for intakes and case exhausts. The blade design moves lots of air which is good for exchanging air inside the case.
Static pressure fans
Static pressure or high mmH2O fans have tight blade spacing to force air through tight spaces and heatsinks. Use them on radiators and CPU/GPU heatsinks.
Check the noise rating in dBA – lower is quieter. 25-30 dBA is virtually silent while 70+ dBA is very loud.
120mm and 140mm are common sizes for case fans. Measure existing fans or fan mounts to ensure compatibility.
3-pin DC fans use voltage control. 4-pin PWM fans can be speed controlled by pulse width modulation.
Use a smoke tester or incense stick to observe airflow direction and volume. Or tape ribbons to visually see the airflow.
Testing static pressure
Hold the fan a few inches from a smooth surface. It should be strong enough to hold a sheet of paper against the surface.
Constantly running computer fans can quickly go from annoying to a serious problem if overheating components are involved. Take time to thoroughly diagnose the root cause, whether it be dust, fan failure, thermal issues, BIOS settings or environmental factors. Getting the fans back under control will lead to a cooler, quieter and healthier PC.