The right solution for your heat pump fault code.

Possible cause:

• Pressure loss in the building circuit due to leakages or air pockets
• Building circuit pressure sensor defective
• Insufficient/no water in the product.
• Fault in the electrical connection for the water pressure sensor
• Cable for the pump/for the water pressure sensor is loose/not connected/defective
• Water pressure sensor defective
• Pump operation interrupted
• Solenoid valve for the automatic filling device defective
• Internal expansion vessel defective

How to fix it:

• Troubleshooting an error code should be left to an expert. Do not attempt to repair the device yourself. Have it done by a professional: Request expert help!

Possible cause:

• Stopcock was not opened
• Building circuit pump defective
• All consumers in the heating system are closed
• Thermostatic valve(s) defective
• No bypass valve available in systems without a buffer
• Bypass valve incorrectly set or defective
• Air in the heat pump
• Pump has insufficient output or is defective
• Condenser is dirty
• Existing dirt filter clogged

How to fix it:

• Troubleshooting an error code should be left to an expert. Do not attempt to repair the device yourself. Have it done by a professional: Request expert help!

Possible cause:

• Pressure loss in the environment circuit due to leakages or air pockets
• Environment circuit pressure sensor defective

How to fix it:

• Troubleshooting an error code should be left to an expert. Do not attempt to repair the device yourself. Have it done by a professional:Request expert help!

Possible cause:

• The integrated high-pressure switch in the outdoor unit has tripped at 31.5 bar (g) or 32.5 bar (abs)
• The integrated high-pressure switch in the outdoor unit has tripped at 46 bar (g) or 47 bar(abs)
• Insufficient energy output via the condenser
• Refrigerant pressure too high

How to fix it:

• Troubleshooting an error code should be left to an expert. Do not attempt to repair the device yourself. Have it done by a professional: Request expert help!
  

Possible cause:

• Heat pump with uniTOWER Split plus: The compressor outlet temperature is above 110 °C: Application limits exceeded, EEV does not work or does not open correctly, Refrigerant volume too low (frequent defrosting due to extremely low evaporation temperatures)
• Heat pump with uniTOWER plus: The compressor outlet temperature is above 130 °C: Application limits exceeded, EEV is not working or does not open correctly, refrigerant volume too low, (frequent defrosting due to extremely low evaporation temperatures)

How to fix it:

• Troubleshooting an error code should be left to an expert. Do not attempt to repair the device yourself. Have it done by a professional: Request expert help!

Possible causes:

• Insufficient air volume flow through the outdoor unit's heat exchanger (heating mode) leads to an insufficient energy input in the environment circuit (heating mode) or building circuit (cooling mode)
• Refrigerant volume too low

How to fix it:

• Troubleshooting an error code should be left to an expert. Do not attempt to repair the device yourself. Have it done by a professional:Request expert help!

Possible causes:

• The temperature in the heating circuit is too low, outside of the operating characteristics
• Refrigerant volume too low

How to fix it:

• Troubleshooting an error code should be left to an expert. Do not attempt to repair the device yourself. Have it done by a professional: Request expert help!

Possible causes:

• Temperature in the environment circuit (cooling mode) or building circuit (heating mode) too high for compressor operation
• Feed-in of external heat into the building circuit
• Refrigerant circuit overfilled
• Insufficient flow rate in the building circuit

How to fix it:

• Troubleshooting an error code should be left to an expert. Do not attempt to repair the device yourself. Have it done by a professional: Request expert help!

Possible causes for heat pumps with uniTOWER plus:

• Internal electronics fault on the inverter PCB
• Mains voltage outside of 70 V–282 V

How to fix it:

• Troubleshooting an error code should be left to an expert. Do not attempt to repair the device yourself. Have it done by a professional: Request expert help!

Possible causes:

• Missing communication between the frequency converter and the outdoor unit's control PCB.

How to fix it:

• Troubleshooting an error code should be left to an expert. Do not attempt to repair the device yourself. Have it done by a professional: Request expert help!

Possible faults:

• Heat pump with uniTOWER plus: The electronics system of the high efficiency pump has detected a fault (e.g. dry running, blockage, overvoltage, undervoltage) and has switched off and locked the pump.
• Heat pump with uniTOWER Split plus: The electronics of the high-efficiency pump has detected a fault (e. g. dry running, blockage, overvoltage, undervoltage) and switched off the pump as a securing measure.

How to fix it:

• Troubleshooting an error code should be left to an expert. Do not attempt to repair the device yourself. Have it done by a professional: Request expert help!

Possible causes:

Heat pumps with uniTOWER plus:

• The sensor is not connected or the sensor input has short-circuited
• Both of the flow temperature sensors in the heat pump are defective

Heat pumps with uniTOWER Split plus:

• Pump does not report any signal back to the heat pump.

How to fix it:

• Troubleshooting an error code should be left to an expert. Do not attempt to repair the device yourself. Have it done by a professional: Request expert help!

The official heat pump fault code list for Vaillant systems is only available from us. You find it at the top of this page. We update it continuously so that it is always up to date. If you don't find your error code here, contact your local partner.

With annual service you can prevent many faults in your heating system. Because experts keep an eye on your device, make sure the settings are correct. In this way, your heating system runs efficiently and safely in the long term. In addition, you can use the myVAILLANT app to conveniently view and optimise all the functions and data of your heating system on your smartphone at any time.

The code F20 means: "The safety cut-out (SCO) interrupts the gas valve control. The gas valve was closed because the temperature of the flow or return temperature sensor has exceeded the maximum limit." To solve the issue please check our recommendation in the official overview list at the top of this page.