What it means
Vaillant's VWZ AI fault table gives 70 V to 282 V as the range for this check, and says the supply should measure between 195 V and 253 V. F.817 (compressor), F.818 (mains voltage) and F.819 (overheating) are more specific frequency converter faults.
What to check, in order
- Note any power problems
If there has just been a power cut or flickering lights, tell your installer. A mains voltage outside the allowed range is one of the causes Vaillant lists.
- Reset once
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
Call your installer. Vaillant's table has them check the power supply and compressor cables and plugs, measure the mains voltage and the phases, and replace the frequency converter if needed.
A repair visit will usually check the compressor, its wiring and the inverter board that drives it.
- 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 F752 error code mean?
The frequency converter, the electronics that drive the compressor, has reported a fault. Vaillant says this is either an internal fault on the inverter board or a mains voltage outside its working range. Vaillant's VWZ AI fault table gives 70 V to 282 V as the range for this check, and says the supply should measure between 195 V and 253 V. F.817 (compressor), F.818 (mains voltage) and F.819 (overheating) are more specific frequency converter faults.
Can I fix Vaillant aroTHERM F752 myself?
Engineer only (engineer visit). Start with: note any power problems; reset once. Call your installer. Vaillant's table has them check the power supply and compressor cables and plugs, measure the mains voltage and the phases, and replace the frequency converter if needed.
Is Vaillant aroTHERM F752 worth repairing?
Get a quote first. If the supply and cables are fine, the frequency converter may need replacing, so ask for a quote before work starts.
Checked against
- Vaillant heat pump appliance interface VWZ AI (for aroTHERM plus VWL ..5/6 A): operating and installation instructions (PDF, 0020291573_01)
- Vaillant: heat pump fault codes
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.