As you can see from below the fan speed is always reported as zero. 
The chip is NCT6791D and the motherboard is Asus X99-E WS.

I don't know if this is a related problem or not but the only fan that shows is
the CPU fan. There are 4 chassis fans that are not shown. All the speeds show
just fine in the BIOS. Fan speed regulation is fine but that's because the BIOS
is doing the controlling, as far as I know.

> sensors
coretemp-isa-0000
Adapter: ISA adapter
Package id 0:  +54.0�C  (high = +87.0�C, crit = +105.0�C)
Core 0:        +49.0�C  (high = +87.0�C, crit = +105.0�C)
Core 1:        +46.0�C  (high = +87.0�C, crit = +105.0�C)
Core 2:        +50.0�C  (high = +87.0�C, crit = +105.0�C)
Core 3:        +43.0�C  (high = +87.0�C, crit = +105.0�C)
Core 4:        +43.0�C  (high = +87.0�C, crit = +105.0�C)
Core 5:        +46.0�C  (high = +87.0�C, crit = +105.0�C)
Core 6:        +44.0�C  (high = +87.0�C, crit = +105.0�C)
Core 7:        +43.0�C  (high = +87.0�C, crit = +105.0�C)

radeon-pci-0700
Adapter: PCI adapter
temp1:        +63.0�C  (crit = +120.0�C, hyst = +90.0�C)

asus-isa-0000
Adapter: ISA adapter
cpu_fan:        0 RPM