Short answer: many power supplies switch the fan off at light loads to stay silent. It’s normal and safe. The fan starts when the unit warms up, usually during gaming. If the fan never spins even under heavy load, that’s when to worry.
How it works
At light loads, a good power supply produces little heat, so it can cool itself without the fan. Once the load or temperature rises past a set point, the fan starts and speeds up as needed. Makers call this zero RPM, semi-passive or fan-stop mode.
When my picks start their fans
| Power supply | Fan starts at about | Source |
|---|---|---|
| be quiet! Pure Power 13 M | 50% load | Club386 |
| be quiet! Dark Power 14 | 70% load on the 1200W model | PC Games Hardware |
| Corsair HXi (2025) | 600W | Tom’s Hardware |
| Seasonic Core GX ATX 3 | Always on: no fan-off mode | Lab reviews |
Switches and knobs
- Some units have a switch on the back to turn fan-off mode on or off. Lab reviewers note the Seasonic Focus GX V4 has one.
- The Corsair RMx (2024) has a knob to set the fan’s minimum speed, according to lab reviewers.
Is fan-off mode bad for the power supply?
No. The unit is designed to run without the fan at those loads, and the fan starts before it gets too hot. Fan-off mode can even help the fan last longer, because it runs fewer hours.
How to tell if the fan has failed
- Run a demanding game for 20 to 30 minutes.
- Look at the power supply fan through the case vent or with the side panel off.
- If it never starts, and the unit feels very hot, the fan may have failed. Stop using it and check the warranty.
Some units have fan failure protection that shuts them down if the fan stops. See power supply protections explained.
- Fan off until about 50% load · Tier Bbe quiet! Pure Power 13 M80 Plus Gold · Fully modular · ATX · 750/850/1000/1200WAlmost silent in two lab tests.Check 850W price
- Fan off until about 600W · Tier ACorsair HXi (2025)80 Plus Platinum · Fully modular · ATX · 1200/1500WQuiet at high power.Check 1200W price
More quiet options in the best quiet power supplies.
Questions
Why is my power supply fan not spinning?
It’s probably in fan-off mode at light load. It should start during gaming.
Should I turn fan-off mode off?
Only if you prefer a constant low fan sound to the fan starting and stopping.
Does a spinning fan mean the power supply is working harder?
It means it’s warmer. The fan speeds up with load and temperature.
Is a power supply without fan-off mode worse?
Not electrically. It’s just never fully silent.
Can I test the fan without gaming?
A stress test that loads the graphics card will warm the unit enough to start the fan.
Sources
- Club386: be quiet! Pure Power 13 M 850W review
- PC Games Hardware: be quiet! Dark Power 14 test (German)
- Tom's Hardware: Corsair HX1200i ATX 3.1 review
- KitGuru: Corsair RM850x ATX 3.1 review
- HWBusters: be quiet! Pure Power 13 M 850W review
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