Abstract: A gas-fired water heater including a water tank, a combustion chamber, a burner assembly disposed within the combustion chamber, a gas valve for controllably supplying gas to the burner assembly, a temperature sensor coupled to the combustion chamber, wherein the temperature sensor generating a signal related to the temperature of the combustion chamber, and a controller having an electronic processor and memory. The controller is configured to receive the signal at a first predetermined time and at a second predetermined time, calculate a change in temperature based on the signal received at the first predetermined time and the signal received at the second predetermined time, compare the change in temperature to a rate of change threshold to produce a first comparison, and shut the gas valve in response to the change in temperature being less than the rate of change threshold.