It gets to 209 very fast and suddenly stalls
I'm pretty pissed about this boilcoil. I went all out n bought a 5000W element that can hardly make a rolling boil
I'm about 99.9% sure the your frustration is misplaced. This is based entirely on the fact that it gets to 209F quickly.
With 5k watts across the line, you should see a rolling boil, even with water and even with the low wattage density of a Boilcoil. And even with 1250 watts (1/4 of 5k) you should see a nice simmer.
Perhaps you should start a new thread to garner some more troubleshooting feedback. You're buried in someone else's thread right now.
In the meantime, going to ask a couple of questions, not to insult, but just to make sure all the boxes are checked.
-Are you in boil mode?
-Did you set bast to 0?