What it means
Vaillant's VWZ AI fault table calls this 'Fan unit 1: Fan blocked'. F.785 is the same message for fan unit 2, with the same advice.
What to check, in order
- Switch off at the breaker
Turn off the circuit breaker for the heat pump before you clear anything. Never put hands or tools through the fan grille.
- Clear the grilles
Vaillant's aroTHERM plus operating instructions say to regularly remove branches and leaves from around the unit and snow from the air inlet and outlet grilles. Vaillant's fix for this code is to check the air path and remove any blockage.
- Switch back on and reset
Restore power and press the reset button on the control module. If the fault comes back after several resets, Vaillant says to contact Customer Service.
When to call your installer
If the air path is clear and the fault returns, call your installer. The fan is not reporting that it turns, so it needs checking by an engineer.
Quick answers
What does the Vaillant aroTHERM F718 error code mean?
The heat pump has had no signal that the fan in the outdoor unit is turning. Something may be in the way, or the fan itself may have a fault. Vaillant's VWZ AI fault table calls this 'Fan unit 1: Fan blocked'. F.785 is the same message for fan unit 2, with the same advice.
Can I fix Vaillant aroTHERM F718 myself?
Easy (about 15 minutes). Start with: switch off at the breaker; clear the grilles; switch back on and reset. If the air path is clear and the fault returns, call your installer. The fan is not reporting that it turns, so it needs checking by an engineer.
Is Vaillant aroTHERM F718 worth repairing?
Usually free. If leaves or snow were in the way, clearing them fixes it. If the air path is clear, it needs an engineer.
Checked against
- Vaillant heat pump appliance interface VWZ AI (for aroTHERM plus VWL ..5/6 A): operating and installation instructions (PDF, 0020291573_01)
- Vaillant aroTHERM plus VWL 35/6 to 125/6 A: operating, installation and maintenance instructions, Nordic edition (PDF, 0020297933_03)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.