This guide is for the Miele S 828, but many Miele (and other brands) vacuum cleaners are very similar on the inside, so that some advice may be helpful elsewhere.

This error presents as follows: Suddenly the vacuum cleaner will stop running and the red indicator light beneath the warning sign to the top left will illuminate.

According to the manual this indicates overheating of the motor. However, this erroneous warning will appear even when the cleaner is completely cold and is caused by a malfunctioning or desoldered overheat bimetal switch.