Boiler shows a general sensor fault; may relate to multiple NTCs or internal sensors.

Safety: Isolate power before opening the boiler.

Steps:

• Visual inspection: Look for any obvious damage to sensor wiring looms, especially where they pass near hot components or sharp edges.
• Check all NTC plugs: Reseat the flow, return, DHW, and flue NTC connectors on both the sensors and the PCB.
• Moisture check: Inspect the PCB area for signs of condensation or water ingress. Address any leaks before further operation.

Professional diagnosis: Because this code can indicate PCB‑level issues, a Bosch service engineer should test sensor circuits and replace the control board if necessary.