Is there air in the heating pipe? One end of the heating pipe is connected to the water inlet of the water pump, and the other end is connected to the water pump outlet. Following the engine water circulation, there will be no air (select the red area for heating and cooling). If you are not sure, you can disconnect the heater water pipe at the water pump inlet while driving. If the water pump end is blocked, install it again after the water in the heater hose comes out.