COMBUSTOR

PROBLEM TO BE SOLVED: To maintain good CO detection sensitivity for a long period of time, by determining the timing of a heat cleaning based on a prescribed measuring time, in the case where a CO detection element for catalytic reaction to CO gas in exhaust gas is suitably raised of the temperature thereof for heat cleaning of the CO detection element. SOLUTION: A controller 14 of a water heater which is a combustor controls the operation of the water heater by a water heater control part 19 via various driving circuits 20 to 22 based on the CO concentration in exhaust gas detected by a CO sensor 16. A CO sensor control part 25 of the CO sensor 16 increases the electric power to a CO detection element 17 by means of a CO detection element driving circuit 24 based on a command signal from the water heater control part 19 for heat cleaning thereof. In this case, the water heater control part 19 is equipped with a fixed time timer 26, in the case where one combustion or more occurred within the fixed time measured by the fixed time timer, heat cleaning of the CO sensor 16 is accomplished by outputting the command signal from the water heater control part 19.