A gas valve, comprising: a plug valve, having a first plug valve gas inlet, a second plug valve gas inlet, a plug valve connection port, and at least one plug valve gas outlet, and configured to assume a closed position where the first plug valve gas inlet is obstructed from the plug valve connection port, a first open position where the first plug valve gas inlet is in communication with the plug valve connection port, and a second open position where the first plug valve gas inlet is in communication with the plug valve connection port and the second plug valve gas inlet is in communication with the at least one plug valve gas outlet; a proportional valve, having a proportional valve gas inlet, a first proportional valve gas outlet, and a second proportional valve gas outlet, and configured to assume a closed position where the proportional valve gas inlet is obstructed from the first proportional valve gas outlet and the second proportional valve gas outlet, and an open position where the proportional valve gas inlet is in communication with the first proportional valve gas outlet and the second proportional valve gas outlet, wherein the plug valve connection port is only in direct communication with the proportional valve gas inlet, and the second proportional valve gas outlet is only in direct communication with the second plug valve gas inlet; wherein the proportional valve and the plug valve have an integrally formed valve body, and the plug valve connection port and the proportional valve gas inlet form an integrally formed connection hole in the valve body; and wherein the second proportional valve gas outlet and the second plug valve gas inlet form an integrally arranged connection cavity within the valve body, and the first proportional valve gas outlet is in communication with the connection cavity. a plug valve, having a first plug valve gas inlet, a second plug valve gas inlet, a plug valve connection port, and at least one plug valve gas outlet, and configured to assume a closed position where the first plug valve gas inlet is obstructed from the plug valve connection port, a first open position where the first plug valve gas inlet is in communication with the plug valve connection port, and a second open position where the first plug valve gas inlet is in communication with the plug valve connection port and the second plug valve gas inlet is in communication with the at least one plug valve gas outlet; a proportional valve, having a proportional valve gas inlet, a first proportional valve gas outlet, and a second proportional valve gas outlet, and configured to assume a closed position where the proportional valve gas inlet is obstructed from the first proportional valve gas outlet and the second proportional valve gas outlet, and an open position where the proportional valve gas inlet is in communication with the first proportional valve gas outlet and the second proportional valve gas outlet, wherein the plug valve connection port is only in direct communication with the proportional valve gas inlet, and the second proportional valve gas outlet is only in direct communication with the second plug valve gas inlet; wherein the proportional valve and the plug valve have an integrally formed valve body, and the plug valve connection port and the proportional valve gas inlet form an integrally formed connection hole in the valve body; and wherein the second proportional valve gas outlet and the second plug valve gas inlet form an integrally arranged connection cavity within the valve body, and the first proportional valve gas outlet is in communication with the connection cavity.