If I want to do Chazara on Shabbos, am I allowed to put the pot down on a pot warmer without holding it and then return it to the hotplate or is this considered like putting it on the ground?
If the pot warmer is hot enough that it can make the food yad soledes bo, then it is permitted, because it is still considered on the fire. If however is not hot enough to make the food yad soleds bo, then it is problematic because you are now moving it from a place that was off the fire to place on the fire.
According to R’ Moshe (Igros Moshe O:CH 4-61) and others (Meohr Hashabbos 1 pg. 530-3, Emek Hateshuva 4-8(8), Halachos of Shabbos pg. 364) we may not move a pot that is on a part of the stove that is not yad soledes to a part that will make the food yad soledes bo because it is considered chazara. Others however disagree with this and permit it basedon the reasoning that it the whole blech is considered one place, and they don’t consider it removed from the fire (Shmiras Shabbos Khilchoso 1 ftnt. 125, Zera Shemuel ftnt. 84). However in this case when it was totally removed from this fire, and it isn’t yad soledes bo, even those poskim might agree that it would be considered chazara. Poskim.