aspire z24-880 All in One fan running full throttle all the time even at low temperature

JACKALPAI

My z24-880 fan goes into full throttle as soon as the computer is turned on today. I installed HW Monitor to check temperature. All 4 Core temperature below 40 degrees C. GPU blow 40 too. Fan at 4000 RPM on boot.
 There are 2 temperature reading for the computer: TMPIN0 41 degree, TMPIN1 80 degree. Is TMPIN1 80 degree the reason that FAN kicked in at full throttle?

It has been quiet for months, and acting weird today. I shut it down for 5 minutes, and restart, same thing happened immediately

Any help will be appreciated. 

 

JACKALPAI

I opened the back cover, removed the heat sink on the CPU, removed the thermos paste and re-applied new thermos paste. Now, both TMPIN0 and TMPIN1 are below 40 degree C. But as soon as I turn on the computer, the fan is on full throttle, at 4000 RPM.

The computer works fine otherwise, but with really loud fan working on max speed.

Now I can rule out high temperature completely. It must be the controller of the fan.

Any suggestions?