Chang'an Star 2 generation heater is not hot. Later, I checked and found that the heater water pipe is not circulating water. I have replaced the heater water tank and water pump, but the water is still not circulating. What is the reason?

Based on what you said, it doesn’t make sense logically, but it’s true. You can try it like this: There are two pipes connected between the engine and the heater water tank. One pipe is for the engine coolant (warm water) to come out and enter the heater water tank, and the other pipe is for the heater water tank to flow back to the engine. First, it will flow from the heater water tank to the heater water tank. Take out the end of the engine that goes into the warm water tank and start it briefly to see if any water comes out? If it says there is no problem with this, then connect the pipe and return the warm water tank to the engine, remove it and start it again to see if there is any water rushing out. If there is water, it means there is no problem with the warm water tank. If not, it means the problem is. The warm water tank is here. If the hot water tank proves to be fine, just connect the pipe. Logically speaking, there should be warm air. However, if there is still no warm air after connecting, it means that the problem is that the joint where the return flow enters the engine is clogged. In short, I will judge and troubleshoot step by step. Maybe I can find the problem. I wish you success. One more reminder, you must have a thermostat core, otherwise you won't have the warm air you imagined.