| 摘要 |
PROBLEM TO BE SOLVED: To avoid firing even when a temperature detection device of a vaporizer has a trouble and hence the vaporizer is at a low temperature. SOLUTION: A period of time from combustion interruption to combustion initiation is measured by first timer means 32 to estimate preheating time required at the lowest for a vaporizer 1. When time required for actual preheating obtained by second timer means 33 is short, combustion is prevented from being started. As a result, even when a thermistor 11 reaches a predetermined temperature earlier than predicted preheating time owing to a trouble of the thermistor 11 of the vaporizer 6 though the vaporizer 1 is actually at a low temperature, the combustion is not started, so that firing is avoided in the state where preheating is insufficient.
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