Water heater exhaust fan won't shut off

My water heater has an external exhaust fan which normally turns on while the water heater is operating. Recently after I had to shut off the water heater to replace a leaky outlet hose, the exhaust fan started operating constantly, whether or not the water heater is operating. An old instruction sheet said to push the two reset buttons in the center of the draft spillage switches, but they don't seem to do anything. Any advice?
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