First of all, the heating function only works if the battery is connected to an active charger. The best I can tell, if it's connected to an active charger, when the BMS senses the temperature has reached your "Charge under temp Trigger Value" setting, it simultaneously turns off the Charging Port and connects the ground to the H- terminal which will turn on your heaters if you have them connected properly. Once the temperature reaches your "Charge under temp Release Value", it disconnects ground to the H- and turns on the Charging Port again.
The problem I am having is that I have some fixed "Gate Operator" batteries connected to mine and these batteries are connected to
Mroinge MBC022, 12V 2A Lead Acid & Lithium(LiFePO4) Automatic Trickle Battery Charger Smart Battery Maintainers
and once the battery is full (which is 99% of the time), the maintainer goes to sleep and the BMS does not sense that it is connected to a charger and the heaters do not activate.
If anyone has figured out a way around this issue please let me know. I am going to start another thread asking just this question.