Vaillant aroTHERM fault F.741

What it means

During de-icing, the return temperature falls below 13 °C. The compressor is blocked while the fault message is present.

Likely causes

1. During the de-icing, the return temperature falls below 13 °C
2. Filling pressure outside permitted range causes flashing indication

Where to start

1. Ensure the minimum installation volume is maintained
2. Activate the electric back-up heater in the product's control panel and in the system control
3. Observe whether the filling pressure bar symbol is displayed statically (normal) or flashing (fault - out of range)