Gas water heater

The invention discloses a gas water heater. The heater comprises: a shell, wherein a containing cavity is defined in the shell, and the shell has a water inlet interface and a water outlet interface; a catalytic combustor, wherein the catalytic combustor is arranged in the containing cavity, a premixing cavity is defined in the catalytic combustor, the catalytic combustor is provided with an air inlet and an air outlet which are communicated with the premixing cavity, a catalyst is arranged at the air outlet, and the catalyst is constructed to conduct continuous combustion when the temperature exceeds the preset temperature and fuel gas and air are supplied; a fan, wherein the fan is communicated with the air inlet so as to convey air to the premixing cavity; a gas proportional valve, wherein an outlet of the gas proportional valve is communicated with the gas inlet so as to convey gas to the premixing cavity; and a heat exchanger, wherein the heat exchanger is arranged above the combustor and connected with