Temp. constant water heater

The utility model discloses a temperature constant water heater, comprising a temperature controller, a temperature sensing device, a flame sensing device, a switch built-up construction and an electronic controlling base plate. Wherein, the switch built-up construction is provided with a firepower pan for adjusting the differential pressure, a temperature constant electromagnetic valve and a main flaming valve with the main flaming valve and the temperature constant electromagnetic valve communicating with the gas inlet pipe and the burner of the temperature constant water heater. While the electronic controlling base plate is electrically connected with the temperature controller, the temperature sensing device, the flame sensing device, a firepower pan for adjusting the differential pressure and the temperature constant electromagnetic valve, which is used for accepting the signals of the temperature controller, the temperature sensing device and the flame sensing device, calculating the demand of the firedamp, transmitting the signals onto the firepower pan for adjusting the differential pressure and the temperature constant electromagnetic valve as well as controlling the quantity of the output firedamp of the main flaming valve and the temperature constant electromagnetic valve.