Helping people with computers... one answer at a time.

Your system fan is an important component of your system. If the fan fails your system could fail or some components could even be damaged.

What does it mean when my computer wont boot up and it says system fan error and check system fan?

Don't get me wrong, I'm not trying to be curt, but the message means exactly what it says: you need to check the fan in your system.

What fan? What's a fan? Which fan? And why?

Fair enough, let's review one of the most under-appreciated components of your system.

Almost every computer has one or more fans that blow air through the inside of the computer case. This is true for laptops as well as desktops. In fact, the system fan is a critical component. If the fan fails your computer may overheat and damage other critical components.

There may be more than one fan.

"... in recent years additional circuitry has been added to computers to allow the computer to monitor the fan ..."

For desktop machines there's typically at least one fan in or near the power supply. The power supply itself can generate a fair amount of heat, and having a fan nearby not only keeps it cool, but also ends up moving air through the rest of your computer's enclosure.

Computer Fans

There may sometimes be a second fan near the front of the computer, just behind the faceplate. This fan, in conjunction with the fan at the back of the computer, helps to keep air moving through the computer. One will push air in, and the other will pull air out.

In some cases there's yet another fan, directly on or over the CPU. The CPU is another source of a great deal of heat. Placing a fan near the CPU itself keeps cooler air blowing over it to help dissipate some of that generated heat.

As I said, the system fan is a critical component. So critical, in fact, that in recent years additional circuitry has been added to computers to allow the computer to monitor the fan and make sure it's working properly.

So, which fan?

On this there's no standard that I'm aware of.

My recommendation: check them all. If your system is failing to boot because of a problem with one or more of its fans, it's important to check it out. You'll need to open the case and see which one isn't working. If you're not comfortable doing that, particularly if you have a laptop, then you'll need to take your machine to a technician for diagnosis.

Article C3073 - July 2, 2007 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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11 Comments
James Mahaffey
July 7, 2007 9:46 AM

I'm glad to see I am not the only one with questions concerning fans. I have a Dell Dimension 3000 computer which starts making alot of noise when the heat goes up. I only see one fan. Am I over looking something? I love this computer but this noise drives me crazy. What can I do other than buying a air conditioner for the room. I have this Multimedia Computer System which also has a Pentium 4 inside. I don't even know the name of this thing. It just shows Phonix on boot. They put 2)fans in this thing. Why wouldn't Dell do the same? If I buy another fan where would I mount it in my Dell? I don't want to blow the thing up. I'm sorry for the length, just want to clearly explain my confusion. Thanks

Bill
July 9, 2007 4:02 AM

Another great Leo article. Readers may care to download SpeedFan, a great little utility for keeping tabs on exactly what's going on. Go to...
http://almico.com/speedfan.php

Tonia
December 13, 2007 8:41 AM

When I try to turn on my computer it will start to boot and then shut down and then start to boot and then shut down....and so on. Can you tell me what this could possibly be?
thanks
Tonia

Leo A. Notenboom
December 14, 2007 12:07 PM

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It could be any of a thousand different things. I'd have you start with this
article:
http://ask-leo.com/why_does_my_computer_randomly_reboot_without_warning.html

Leo


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Bren
January 19, 2009 12:59 PM

Okay, my computer won't boot up and says "check system fan, system fan failure." I have no problem checking it out and mine has 3 fans and all three are working, yes I have cleaned them all also so why do I keep getting this message if my fans are all in working order?

There's no way to know for sure without looking at the computer, but typically the connection to the sensor that monitors the fan, or the sensor itself, is broken. Could be other things, but that's most common.
- Leo
20-Jan-2009

Pat
April 27, 2009 7:25 PM

My fan was running constantly. I restored the system to an earlier point and it seemed to go back to normal. Now it doesn't sound like it is running. There are 2 fans in my computer. How do I check to make sure they are running?I don't want to burn the computer up.

anca
July 8, 2009 12:58 AM

I`ve got a warning! from easy tunes program :system fan=0.Please help me.Thanks!

Malcolm Walters
March 16, 2010 8:04 AM

I changed the battery in my computer now when I start it I get "CPU Fan failed" (but the fan is running) press F2 to enter bios however it shuts down before I can get into the bios. Can you suggest some way to get this fixed?

Paul Clarke
December 24, 2011 12:37 PM

You mention having a fan over the CPU blowing cool air on it. While this is not the worst thing in the world, in 80% of cases ("cases" excuse the play on words) it's far better to have a fan taking hot air AWAY from the CPU.

The CPU heatsink and fan are pushing air in a specific direction - a fan blowing TOWARDS that is actually acting counter to the CPU's own fan. There is also the issue of blowing external dust and other particles directly onto the heatsink and CPU fan from outside the case.

Above the CPU have a fan blowing air out.

With modern high perfomence design or gaming GFX cards I would not go into the fray without at least 2 120mm fans - preferably 3 or even more.

One surprisingly good ploy is to have two side by side at the back of the case, the bottom one sucking air in, the top one blowing air back out.

In fact I would only even have one "input" fan on just about any set up. and then 2 or 3 output fans.

Rapid 120mm fans are great.

Finally, many cases have a lot of obstruction between the front input fan and the main heat generating area of the MOBO (HDD bays, lighting, cabling, optical drives, the butt end of a GFX card etc etc) It's often better to have fans on the back of the case where air flow between it and the components it is trying to cool is less obstructed.

Just to re-iterate though. ONE input fan (the lowest fan vertically) and 2 or more exhaust fans - set HIGHER than the input fan (remember - heat rises)

Great advice regarding cooling here though.
I've seen many a computer needlessly damaged for want of a couple of fans that probably wouldn't cost more than $15 for the lot.

Oh and DON'T PUSH YOUR PC INTO A CORNER - HAVE SOME AIR FLOW AROUND IT.

Paul

Lee
January 4, 2012 12:46 AM

I have a system fan has failed, get it serviced.
my cpu and case fan both work but sounded like it was the case fan so i took it out but still there now i think its the cpu fan but it works it just goes high and low on the sound and sometimes makes a blender noise. how do i fix it so is does not brake as i have has it sent to hp during the first 3 to 5 months i had it because it got so loud and grindy that it finally did not power up even to the bios and when i got it back it has worked until last year and i think those aio boot disk with pe on them are corrupting the hardware as they replaced the motherboard and hard drive but i tried to take the hot melted thermal compoun d of of the cpu and stil not doing right. Thanks for reading all of this and please reply asap. bye.

Gaurav
January 8, 2012 7:26 AM

Hey when i start my system it wont boot up and it is saying that sys fan-N/A. what should i do

Get the system fan repaired.
Leo
09-Jan-2012

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