40 — NTC return sensor faulty

What does 40 mean?

The NTC return sensor, which measures the temperature of water returning to the boiler, is defective or has a wiring problem. This affects the boiler's ability to monitor system temperature.

• Faulty NTC return sensor
• Broken or shorted sensor wiring

Click steps to track your progress.

1. 1

   Press and hold down the Reset button for 2 seconds to try clearing the fault.

2. 2

   Ensure the boiler's power supply is stable.

3. 3

   If the fault persists, contact an Authorised Service Centre to check the sensor and wiring.