Sometimes you can just cover the pot (heat off) and leave it for 15-45 minutes, come back and like magic, you have coagulation! Try a couple of things before you resort to dumping out your milk.
Check that your rennet is fresh- it loses power when left at room temp or kept for a long time. See your kit for a best by date. Visit our shop for fresh rennet.
Check that your thermometer is reading accurately. Without some warmth, your rennet will not activate. Place it in an icy cup of water- does it read 32F? If not, adjust it until it does.
Are you making a fast goat cheese or ricotta from our kits? Small curds are not unusual with fast goat cheese and with ricotta in general. If you use fine cheesecloth to strain, you should end up with nice creamy cheese.
Do you possibly have Ultra-pasteurized milk? If you weren’t after ricotta or goat cheese and your curds never progressed, you probably have ultra-pasteurized or ultra-heat pasteurized milk on your hands. From what I understand dairies are not required to label this milk as such and you should know that even organic dairies are doing this to the milk for longer shelf life. I have found my good milks by trial and error and have actually called customer service phone lines to ask. This has worked well for me. Just a note though, I have found most of my “errors” still resulted in a cream cheese that was nice. Taste yours and use it!