The problem is, the automatic fan control is not working. Clearly, the fans are not defective (and they are very clean). If I set the idle fan speed to maximum, the CPU stays at a temperature of less than 60 degrees C even under full load but the noise is unacceptable. A low fixed speed is suitable for most applications, but under full load (as tested with Prime95), the CPU temperature can exceeed 75 degrees C. The case fan and CPU cooling fan always run at idle speed, depending on the speed I set for them under the 'Thermal Option' in the BIOS. I installed Windows 8.1 Pro with the original HP disks, using the embedded Windows 8.1 product keys. I don't know how the machines accomplish automatic control, but there is no option to change any settings related to that. HP documentation states that this option only controls the minimum idle speed of the fan, and the fan speeds are 'automatically controlled'. Under the 'Power' options tab, there is an option called 'Thermal' which allows you to set the minimum idle speed of the fans. The BIOS setup program for the latest L02 BIOS dated 4/19/19 offers limited options for thermal control. The case fans and CPU cooling fans are original equipment and they are capable of operating at variable speed when connected to a 4-pin PWM connector. I have the same problem with both of them, so I feel that there is unlikely to be an identical hardware failure in both of them. I have two different machines that are virtually identical. Business PCs, Workstations and Point of Sale Systems.Printer Wireless, Networking & Internet.DesignJet, Large Format Printers & Digital Press.Printing Errors or Lights & Stuck Print Jobs.Notebook Hardware and Upgrade Questions.

Bios fan speed control