If my oven is set on a timer to keep food hot, can I open and close it on Shabbos while it’s still on?
When the oven door is opened, the thermostat will detect the cold air that rushes in and will activate the heating element if it is off at that moment. It is forbidden to cause this to occur, even if all the food will be removed all at once before the oven door is re-closed.
[If the oven door is re-closed with some of the food remaining inside, there may be additional concerns of Bishul on Shabbos, depending on the circumstances.]
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