Heating issue

[Confused s212 owner]

Hi, im very new to this webside, and im so sorry if i poste the wrong thing on the wrong place, but im beat, my heater is living its own life, sometimes it works sometimes it dont, last time it happened i was driving and i stopped the car because i was grabbing a bite to eat, then i started the car again and i had fog on my windows so i started the heater and putt it on full, and the fan didn start up, heat was coming out of the ducts but the fan wasnt starting, so today i pulled it out and cheaked it, works fine, no clue what to do ( sorry for my grammar, im from norway so english is not my strong side) any questions ill be happy to awnser or clarify