Hi guys my ball python didnt eat for the last 3 weeks after how long should i force feed?

i've had the bp for 1 and a half year it happened once he didnt eat for a week but he did the next week , first time he's been on 3 weeks without eating and i'm kinda getting worried , everything in the cage is normal the temps are fine he's acting normal too nothing changed but for some odd reason he doesnt want to eat :\

thanks for your answers