When we take a bath, what we are most concerned about is whether the temperature of the hot water is stable. This involves the constant temperature function of the gas instant water heater. The constant temperature function of the gas water heater is when the inlet water flow and inlet water temperature change, the outlet water temperature of the gas water heater can be maintained at the set temperature.

In fact, the way to accomplish it is easy to understand. A flow sensor is used to sense the water flow signal and converted it into an electrical signal to inform the CPU. The CPU can adjust the gas flow accordingly, so that it changes in direct proportion to the water flow to achieve a constant temperature effect. Therefore, in order to achieve constant temperature, we must not only control the gas, but also control the amount of water.

Control gas only: this control method is realized by gas proportional valve, that is, according to the difference between the outlet water temperature and the set temperature and the water flow, it adjust the opening of the gas proportional valve to match the water flow. This can indeed achieve constant temperature, but there are also two problems:

1. If the water temperature is low and the water flow is large, even if the gas proportional valve is fully opened, it will not reach the set temperature, after all,restricted by its maximum power;

2. The controlled temperature is not accurate enough, Usually around 1°C.

Control both gas and water flow, that is, a gas proportional valve regulates in-flow gas, but also a water control device adjusts the water flow. There are two ways in terms of different water control devices.

Memory alloy water flow control device，takes advantages of the mechanical characteristics of memory alloy spring to control the water flow. It can maintain different shapes at different temperatures. Let's take a practical example, it would be much clearer to all. Taking a 10L hot water heater as an example, when the inlet water temperature is 15°C, the memory alloy will control the valve to open to the maximum, which can provide a flow of 10L water. But if in winter the temperature is low, assuming that the inlet water temperature is 10°C, it is not only necessary to open wide the gas proportional valve, the memory alloy will also shrink, there would be only 8 litre of water flow per minute, though the water temperature still maintain constant. However, this would cause another problem, that is, to maintain constant temperature, water flow will have to be reduced.

The other type is to replace memory alloy with water volume servo. Memory alloy realizes control by means of its mechanical structure, while water volume servo makes control more accurate by using motor. With water volume servo in place, temperature accuracy is within 0.1℃. Therefore, gas water heaters equipped with water volume servo are good for high rise buildings or houses bothered by unstable water pressure.