The heater does not produce hot air after the engine has warmed up.
A strange smell becomes noticeable after switching on the heating.
The fan does not work or only works in one mode.
You discover a coolant leak.
The system is louder than usual and makes crunching and crackling noises.
Air bubbles or low coolant level. Park your car on a flat surface and let the engine cool down. Open the hood. Remove the coolant expansion tank cap. Check the coolant level and refill if necessary.
Defective thermostat. Start the engine. Check the lower radiator hose as soon as the temperature display shows more than zero. It should be cold. If it warms up immediately, there may be a fault in the thermostat. Check the lower radiator hose as soon as the coolant reaches 85 ° C. It should be warm to hot. If it is still cold, the thermostat may be defective.
Clogged heat exchanger and pipes. Clean dirt and foreign objects from the heat exchanger. Remove the heat exchanger and wash it off with a special agent.
Defective fan motor. Check the circuit, especially the contacts. Make sure the carbon brushes and heater fan bearings are not worn.
Defective heating control valve or heating flap. Check the heating control valve or the heating flap visually. If you find that the control valve lever is rusted, the rubber seals are dry, or the heater control valve or hatch is worn out, replace these components.