Cause of error code d5

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.

Solution for error code d5

- 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, reset the IPM 2 (if installed) to the factory default settings and carry out the automatic system configuration.