What are the reasons for the car's heater not producing heat?

[StFelicity]

Here are the detailed reasons why the car's heater is not producing heat: 1. The thermostat is constantly open or opens too early, causing the cooling system to enter the major circulation prematurely. Since the external temperature is very low, the engine coolant temperature cannot rise, and the heater will not produce heat. 2. The water pump impeller is damaged or slipping, resulting in insufficient flow through the heater core, preventing heat from being delivered. 3. There is an airlock in the engine cooling system, which disrupts proper coolant circulation, leading to high coolant temperature and a non-functioning heater. If there is always air in the cooling system, it is likely due to a damaged cylinder head gasket allowing combustion gases to enter the cooling system. If the inlet pipe of the heater core is very hot while the outlet pipe is relatively cold, this indicates a blockage in the heater core, and it should be replaced.