generally speaking (no halachical responsibility accepted) –
– the blech should cover flame and controls (or controls can be covered seperetaly by alfoil etc)
– if you take a pot off and put it down on a surface you can not put it back on
– if the food is fully cooked then if you hold the pot in your hands while someone else takes food out of the pot you can then return it to the blech
– you can put cooked cold food on top of a pot which is on the blech to warm it up becuase ein bishul achar bishul
– you can move pots around on the blech so long as the area in which you are moving the pot around is over yad soledes bo (approx 70 celsius)