F.84 — Fault: Flow/return temperature sensor temperature difference implausible

What does F.84 mean?

The boiler's flow and return temperature sensors are reporting implausible or inconsistent temperature differences. This could be due to incorrect installation or faulty sensors.

• Flow and return temperature sensors have been inverted (swapped).
• Flow and return temperature sensors have not been correctly fitted to the pipes.
• One or both sensors are defective.

Click steps to track your progress.

1. 1

   Press the fault clearance key on the boiler to reset it.

2. 2

   If accessible, visually check that the flow and return sensors appear to be correctly installed on their respective pipes.

3. 3

   If the fault persists, contact Vaillant Service Solutions to inspect the sensor installation and function.