BMW Inline Instructions De Montage page 133

3. 1 5 To service the auxiliary heater
The auxiliary heater should be checked at a BMW service centre at regular intervals, at the latest when the weather
starts to turn cold.
Refer to the instructions in the owner's handbook.
To avoid starting problems caused by using the auxiliary heating system, you should not use the auxiliary heating
system if you only drive the car for short distances (< 20 km).
When the auxiliary heating system is not in use, the heater is to be run for 10 minutes every four weeks to prevent
the auxiliary heating system suffering from starting difficulties when you next need it.
Subject to technical modifications.
3-90/EN