In fact, the damper of hot-cold conversion is not open to the hot air, and then we need to see if there is something blocking the hot air tank, and some hot-cold conversion dampers are covered with a layer of sponge. I have encountered the situation that this layer of sponge fell off and stuck to the hot air tank, which caused the hot air not to blow out.
Furthermore, the water pipe of the small water tank is hot, but the water tank is not necessarily hot. You can start the car and turn on the heating. If there is still a little warmth in the air duct at first, it will be gone after a while, and it will become cold. It may be that Num enjoys congestion.