Blech on a gas stove

Hi,

Even if a gas burner is entirely open, such that the flame could not be raised, it must be covered if one wishes to leave food on the burner from before Shabbat. This is for several reasons, including:

1. We do not distinguish between burners which could and could not be raised, and
2. One might accidentally lower the flame and then raise it later.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 4:74:Bishul 25)

המצפה לישועה,
Mordechai