A gas flow controller for use in a gas-fired apparatus including a pilot burner and a main burner is provided. The controller includes a housing defining a diaphragm chamber, a pilot valve operable to open and close a first fluid flow path between a gas supply inlet of the gas flow controller and the diaphragm chamber, and a main burner valve operable to open and close a second fluid flow path between the gas supply inlet and the main burner. The main burner valve includes a diaphragm that is disposed within the diaphragm chamber and includes a central portion and an annular outer portion. The outer portion is configured to deflect into engagement with the housing to close a third fluid flow path in response to an over-pressure condition at the gas supply inlet.