Gas water heater is a kind of water heater that uses gas as the main energy material, and the high temperature heat generated by gas combustion is transferred to the cold water flowing through the heat exchanger to achieve the purpose of preparing hot water. Gas water heater is the mainstream water heater that once occupied water heater market, its advantage is namely open namely use with, need not wait, and cover an area of an area lesser, can save a lot of space for the comrades that reside in day dynasty. In terms of safety, the gas water heater achieves the separation of heat generation and heating. The bath is in the bathroom and installed in the kitchen, avoiding the danger of electrical leakage generated in the bath process. The disadvantages of gas water heaters are also obvious. It should not be installed in the bathroom or far from the kitchen above all, because in principle, gas water heater is not installed in the bathroom, if far from the kitchen, hot water pipeline is too long, the middle will be wasted a lot of water resources. Additional, inconvenient place is user cannot oneself adjust temperature in washing bath process, and must be in before entering the bathroom the temperature had been adjusted first, and temperature can be hot and cold, the constant temperature water heater of gas that appears nevertheless solved this problem. Gas water heater can also occasionally hit the problem of fire.