A gas-fired cooking grill and a gas valve assembly for a gas-fired cooking grill are provided. The grill includes a cooking chamber, a plurality of gas burners for heating the cooking chamber, a plurality of first valves each to control flow of a combustible gas to a respective one of the gas burners, a gas intake to receive the combustible gas from a combustible gas source, and a second valve comprising a thermostatic valve portion, the second valve disposed intermediate the gas intake and plurality of first valves and in fluid communication therewith, the second valve configured to receive input from a user for selection between a first cooking mode and a second cooking mode, the second valve routing the combustible gas from the gas intake to the plurality of first valves in the first cooking mode and routing the combustible gas from the gas intake to the thermostatic valve portion in the second cooking mode, the thermostatic valve portion selectively routing the combustible gas to a subset of the gas burners based on a comparison of a desired temperature and an actual temperature of the cooking chamber.