Is the fan actually stopped, or is this just a reading of 0 RPM?
And to add, this isn't adding burden to the other fan or the pump...at all.
yes. and i have to use a pen to touch it. then it spin again.So, is the fan actually stopped, then?
Sounds like either the fan curve is set incorrectly so that fan does not stay in a running state, or there is an issue with the fan. Are the fans running from a splitter (1 wire that controls 2 fans?) or are they defined separately? If separately, if you swap the fan control wires, does the other fan then work in a limited capacity like the original, or does it work correctly at all times and how does the currently 'broken' fan work?