Abstract: Food products are cooked by immersing them in a body of hot liquid contained in a vat, and in order to maintain the liquid at a temperature level suitable for cooking purposes a gas burner underneath the vat is turned on periodically. Gas consumption is conserved, each time the gas burner is turned off, by interrupting the air passageway associated with the burner, to prevent cold air from flowing through the passageway and hence drawing off the heat energy that was previously stored in the body of hot liquid.