External supply temperature sensor defective (low-loss header).
The external supply temperature sensor was recognized on the BUS and then reconnected to the appropriate terminal.
Check temperature sensor and leads for interruptions or shorts, and replace if defective.
Check whether only one temperature sensor is connected; otherwise remove second temperature sensor.
Reset the boiler to the factory default settings ( service function 8.E), reset the IPM 2 (if installed) to the factory default settings and carry out the automatic system configuration.
