Chapter in this post:
So far I always thought that it was due to a defective or incorrectly connected temperature sensor when the IMac fan is running at full speed. Today, however, I learned that it could also be due to something else - completely unexpected.
But first a little story: My stepdad has an older iMac that was completely sufficient for him. It has been running smoothly for years, but suddenly it started running the fans at maximum speed. This is always a sign that something is wrong.
My recommendation was to restart the Mac. But this has already been done several times and was unsuccessful.
After the fan problem did not go away, but you could actually still use the Mac, something new was added: Suddenly the mouse and keyboard stopped working so that the iMac could no longer be operated. Now it was really time to act ...
After I couldn't diagnose remotely and the usual keyboard shortcuts didn't bring any improvement, my stepdad was already mentally about to buy a new iMac.
He was about to get an Intel iMac, but luckily he called me again before buying it. That gave me an opportunity to tell him about the new M1 iMacs to report that are definitely the better choice. They're cheap, have a fast, energy-saving processor, and they look very good too.
Only the two USB C ports would have been a problem with my stepdad, as he still has some devices with USB A plugs. I had therefore told him that he should take photos of all the plugs and sockets on his current iMac so that the Apple employee knows which adapters he still needs.
It was funny that unplugging all the USB devices obviously brought the solution. Because after all the photos were taken and the devices were plugged in again, the iMac booted up and everything was the same: the fans were quiet and the mouse and keyboard worked again.
On the one hand it is a shame, because I would have loved to take a look at one of the new M1 iMacs in the wild, but on the other hand good, because my stepfather can still work with the current iMac for a few more years.
The iMac is easily sufficient for word processing with Pages, e-mails and one or the other photo editing.
If your fans are spinning completely and are constantly loud, try a few weird things, like unplugging the external devices. Maybe it will help with you too.
If that's not the case and you just happened to have an SSD built into the iMac, then I recommend you this post as further reading.
Jens has been running the blog since 2012. He appears as Sir Apfelot for his readers and helps them with problems of a technical nature. In his free time he drives electric unicycles, takes photos (preferably with his iPhone, of course), climbs around in the Hessian mountains or hikes with the family. His articles deal with Apple products, news from the world of drones or solutions for current bugs.