Vaillant F83 Fault

Vaillant F83 Fault

The Vaillant F83 error code signifies a flow and return temperature sensor fault. This error occurs when there is a discrepancy or mismatch between the temperatures detected by the flow and return sensors in the heating system, indicating that the system is not operating as efficiently as it should or that there’s a fault with one or both of the sensors.

Causes of the F83 Error Code

  1. Faulty Temperature Sensors: One or both of the temperature sensors might be faulty, providing inaccurate readings to the boiler’s control unit.
  2. Improper Sensor Installation: If the sensors are not correctly installed or have become dislodged, they may fail to accurately measure the water temperature.
  3. Sludge or Scale Build-up: Accumulation of sludge or scale in the system can affect water circulation and temperature distribution, leading to discrepancies between the flow and return temperatures.
  4. Airlocks in the System: Air trapped in the heating system can also cause uneven heating and affect the accuracy of temperature readings.
  5. Pump Failure or Issues: A malfunctioning or incorrectly configured pump can lead to inadequate water circulation, affecting the temperature balance in the system.

Troubleshooting and Resolving the F83 Error Code

  1. Check and Replace Temperature Sensors: Inspect both the flow and return temperature sensors for any signs of damage or malfunction. Replacement of faulty sensors should be carried out by a Gas Safe registered engineer.
  2. Ensure Correct Sensor Installation: Verify that both sensors are correctly installed and securely positioned. A professional can adjust or reinstall the sensors if necessary.
  3. System Flush: If sludge or scale is suspected, a system flush may be required to clear out the buildup and restore efficient circulation. This task should be performed by a professional.
  4. Bleed Radiators and the System: Release any trapped air from the radiators and the heating system to eliminate airlocks and ensure even heating.
  5. Inspect and Repair the Pump: Check the pump for any signs of failure or incorrect settings. The pump may need to be repaired or replaced to ensure adequate water circulation.
  6. Professional Diagnosis: Given the complexity of diagnosing and fixing the F83 error, involving temperature sensors, water circulation, and system cleanliness, professional assistance is recommended. A Gas Safe registered engineer can provide a comprehensive diagnosis and appropriate repairs.
  7. Regular Maintenance: To prevent future occurrences of the F83 error and other potential heating system issues, ensure your boiler and heating system receive regular professional maintenance. This can help identify and address wear and tear, sensor accuracy, and circulation issues before they lead to faults.


The Vaillant F83 error code highlights a significant issue with the temperature sensors or the heating system’s water circulation. Addressing this error requires a thorough inspection and possibly the replacement of sensors, system flushing, or pump repairs. Due to the technical and safety considerations, these tasks should be performed by a qualified professional, underscoring the importance of regular maintenance to ensure the efficient and safe operation of your heating system.