Using a blech on Shabbat

According to Ashkenazim

1. It’s permissible to return a pot of fully cooked food that was previously on a fire to a blech (which doesn’t have an adjustable temperature) as long as one had intent to return it to the fire when the pot was removed, one kept the pot in one’s hands, and the food is slightly warm.
2. It’s forbidden to place a pot of fully cooked food on a blech even if one’s intent is just to remove it’s chill. However, it is permissible to place of fully cooked food on a blech on the area where it doesn’t reach 113 degrees. However, some say that it’s permissible to put foods on the blech on shabbat which could not be cooked on the blech (such as challah or kugel) as long as one doesn’t put it on the area which is over the fire.
3. One may move pots from a cooler area to a warmer position on the blech only if the food is fully cooked and the area from which it stood originally was 113 degrees.

According to Sephardim

1. According to Sephardim, it’s permissible to put a solid (completely) cooked food on top of a blech or hotplate on Shabbat.
2. According to Sephardim, it’s forbidden to put a cooked liquid on a blech or hotplate on Shabbat unless one fulfills the conditions of Chazara, however it is permissible to ask a non-Jew to put a cooked liquid on top of a blech or hotplate on Shabbat.