Today when i turn on the heater the fan does not come on! any reason for it?

 

Check your fuses.

 

You are aware that the blower doesn't run in for heating in "auto" until the engine water jacket temperature reaches 130F? Or in cooling until the A/C evaporator is somewhat cooler than the surround?

Other than that the blower motor has two supply circuits, if you manually put it on highest speed a relay is used to bypass the electronics circuits. Otherwise it probably is a fuse but that would likely mean that the blower motor has stalled or failed in some manner.