Because of carbon deposit, it was blocked at the corner. Because it is a dead bend, there is no way to dig it out. Irrigation baking soda water, with U-tube irrigation for one day. Press the U-shaped mouth upward and put it in the refrigerator for one day. Thaw naturally after taking out, drain water and air dry for several days. Recharge, freeze, control water, air dry, repeat several times, and it will pass. Stupid way, helpless move.