That's the official answer i got from asus i m just posting it for reference to other readers :
Thank you for contacting ASUS Customer Service.
My name is Penny. It's my pleasure to help you with your problem.
The motherboard temperature is in the normal range. If it is below 60C degree, it is normal. You don't need to worry about it. If you want to decrease the motherboard temperature, you can add on another chassis fan to use, and check your chassis whether its air flows well.
If you have any problem, please refer FAQ(Frequently Asked Questions) or contact us again. We will try our best to help you.
It will be very kind of you to mark this mail to show us your satisfaction so that we can improve our service quality with your kindly feedback.
ASUS Customer Service Center(China)
I think as well there is a problem with the sensor because ASUS PROBE is crashing once a while and the readings sometimes are wrong. Anyway I installed a case fan just to be sure and i got my temperature bellow 42 now so for me the issue is over.
Thanks again for the great help mate