The fan error occurs when the computer checks the CPU and Graphics chip cooling fan on startup. It checks whether the fan is spinning fast enough. So in most cases, the fan is not spinning and it will not cool the computer sufficiently.
In a small number of cases, the fan might not be replaced because there is an obstruction in the fan, otherwise, it is true that the heatsink and fan will need to be replaced.
You can contact the CNS Helpdesk to see about checking the CPU heatsink/fan.
Hardware Support Specialist