What it means
Vaillant's VWZ AI fault table says the switch in the aroTHERM plus outdoor unit trips at 41.5 bar (gauge). Vaillant's general heat pump fault code page quotes 31.5 or 46 bar, so the figure depends on the model.
What to check, in order
- Reset once
Press the reset button on the control module. Vaillant's remedy includes resetting the high-pressure switch itself as well as the product, so a reset at the control may not be enough.
- Book your installer if it returns
This is a refrigerant safety fault. If it comes back after several resets, Vaillant says to contact Customer Service.
When to call your installer
Call your installer. Vaillant's table lists too little heat being taken away through the condenser, low water flow and high refrigerant pressure as causes. The engineer checks the dirt filter, the high-pressure switch and sensor, and in cooling mode checks the fan unit for dirt. 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 F731 error code mean?
The refrigerant pressure in the outdoor unit got too high, so the built-in high-pressure safety switch has tripped. Vaillant's VWZ AI fault table says the switch in the aroTHERM plus outdoor unit trips at 41.5 bar (gauge). Vaillant's general heat pump fault code page quotes 31.5 or 46 bar, so the figure depends on the model.
Can I fix Vaillant aroTHERM F731 myself?
Engineer only (engineer visit). Start with: reset once; book your installer if it returns. Call your installer. Vaillant's table lists too little heat being taken away through the condenser, low water flow and high refrigerant pressure as causes. The engineer checks the dirt filter, the high-pressure switch and sensor, and in cooling mode checks the fan unit for dirt. Refrigerant work needs an F-gas certified engineer.
Is Vaillant aroTHERM F731 worth repairing?
Worth fixing. The cause can be as simple as a blocked dirt filter on the water side, or a fault in the refrigerant circuit. The engineer's diagnosis decides the cost.
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.