The outer flame hole 20 and the internal combustion chamber 22 are formed by the burner cap 2 mounted on the annular burner head 11, and the flame sensor 3 is connected to the secondary air supply communication port 15. In the furnace furnace directed toward the internal combustion chamber 22, the exhaust gas sucked into the central air passage 25 of the burner cap 2 at the initial stage of ignition is flowed back into the internal combustion chamber 22 through the communication port 15. To prevent,;A cylinder 7 protruding downward from the lower end of the inner diameter of the burner head 11 is provided to prevent the exhaust gas from flowing shortly from the lower end of the inner diameter to the vent 15.
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