Heater blows intermittent Hot & Cold

Mr_Paint

The past few weeks my heater will work fine & the next day it just blows Cold so after turning it on & off a few times it will usually start blowing Hot again. Now the on-off trick isn't working as well because today I did it at least 10 times & shut off the car a few times as well & then it finally started blowing Hot again. Is there a sensor or something that controls this issue? Pretty sure this is electrical because once it turns on it works fine for the entire drive.
Thanks for any help you can offer.