What it means
Vaillant's VWZ AI fault table words it 'Sensor fault: high pressure'. F.703 is the matching fault for the low-pressure sensor.
What to check, in order
- Reset once
Press the reset button on the control module. If the fault comes back after several resets, Vaillant says to contact Customer Service.
- Book an engineer
The sensor is part of the sealed refrigerant circuit, so don't open the outdoor unit.
When to call your installer
Call your installer. Vaillant's remedy is to check the sensor, for example with an installation aid, replace it if necessary, and replace the wiring harness if needed. Refrigerant work needs an F-gas certified engineer.
A repair visit will usually check the refrigerant charge and the pipe joints for leaks, which needs a qualified refrigeration engineer.
- Note the model and serial number. They're on a label on the rating plate on the outdoor unit, and on the indoor unit or cylinder.
- Write down the exact code, and what the appliance was doing when it appeared.
- Check whether it's still under warranty. If it is, the repair may cost you nothing.
Quick answers
What does the Vaillant aroTHERM F546 error code mean?
The heat pump is not getting a usable reading from the refrigerant high-pressure sensor. Vaillant says the sensor is either not connected or its input has short-circuited. Vaillant's VWZ AI fault table words it 'Sensor fault: high pressure'. F.703 is the matching fault for the low-pressure sensor.
Can I fix Vaillant aroTHERM F546 myself?
Engineer only (engineer visit). Start with: reset once; book an engineer. Call your installer. Vaillant's remedy is to check the sensor, for example with an installation aid, replace it if necessary, and replace the wiring harness if needed. Refrigerant work needs an F-gas certified engineer.
Is Vaillant aroTHERM F546 worth repairing?
Worth fixing. Vaillant's listed causes are the sensor and its wiring, so this is normally a sensor or wiring repair by an engineer.
Checked against
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.