F.1 — Return–NTC open circuit

What does F.1 mean?

The boiler has detected an open circuit in the return NTC (Negative Temperature Coefficient) sensor. This means the sensor is either broken or its wiring connection is faulty, preventing accurate temperature readings.

• NTC sensor broken.
• NTC sensor cable broken.
• Defective connection at NTC sensor or at the main electronics.

Click steps to track your progress.

1. 1

   Reset the boiler by pressing the reset button.

2. 2

   Check for any obvious loose connections if you can safely access them (power off first).

3. 3

   If the error persists, contact a qualified service technician to inspect or replace the return NTC sensor and its wiring.