Is there any way, that one may add hot water from the urn to the crockpot of chulent on Shabbos…(e.g. like if the crockpot is set on low..and we see it is all dry on Shabbos morning)
Before answering your question, the heating element of the crock pot should preferably be covered with thick silver foil, or a few layers of plain silver foil, to serve as a “blech’. This is for two reasons. The first is that there is a prohibition to leave uncooked food on an uncovered flame even from before Shabbos, (called shehiya). The reason is that one may come to improve the heat to help speed up the cooking process (i.e. stir the coals to make them hotter). However, if one has a “blech”, it is permitted to leave the food cook, even if the food in the crock pot is not fully cooked before Shabbos. The second reason is for a situation when you want to remove the pot from the fire and then put it back, called chazora lit. “returning” the pot to the fire. If the fire doesn’t have a blech we may not do chazora.
If you have a blech you may lift the pot, and pour hot water from a different pot, (if it is a pareve urn or pot, keep a distance between the two, so the smoke doesn’t go from one to the other).
Orach Chaim 253-2.