Set the high one first. When the high-pressure safety door is set, the low-pressure safety door will be locked. After the high voltage is set, it is set from high to low. In this process, the set safety door is no longer disturbed by the outside world, and the reliability of the door is high (if it is set low first, it will experience locking after setting); From a safety point of view, setting the maximum pressure of the safety door is equivalent to the boiler not having a reliable safety door to prevent overpressure. When the set value is low, there are some safety doors to prevent the boiler from overpressure. If the setting from low to high is equivalent to the total time of each exit, there is no exit.