Vaillant F27 Fault

Vaillant F27 Fault

The Vaillant F27 error code is indicative of a flame detection fault when there is no flame present. This situation arises when the boiler’s control unit receives a signal suggesting that a flame is detected, even though the boiler has not initiated the ignition sequence or the flame should not be present. This discrepancy can be caused by several factors, primarily related to the flame detection system or electrical interference.

Causes of the F27 Error Code

  1. Faulty Flame Detector: The flame detector, which senses whether a flame is lit in the burner, could be malfunctioning, sending incorrect signals to the boiler’s control unit.
  2. Electrical Interference: External electrical interference or issues within the boiler’s electrical system can cause false flame detection.
  3. Control Board Issues: A fault within the boiler’s printed circuit board (PCB) could result in erroneous readings or signals being interpreted as a flame presence.
  4. Dirty or Misaligned Flame Sensor: Over time, the flame sensor can become dirty or misaligned, which might cause it to incorrectly signal the presence of a flame.

Troubleshooting and Resolving the F27 Error Code

  1. Inspect and Clean the Flame Detector: First, check the condition of the flame detector. If it’s dirty, carefully clean it. Ensure that it is also correctly aligned according to the manufacturer’s guidelines.
  2. Check for Electrical Interference: Look for potential sources of electrical interference near the boiler and eliminate them if possible. Ensure that all electrical connections within the boiler are secure and in good condition.
  3. Reset the Boiler: Attempt to reset the boiler to see if the error persists. Sometimes, a simple reset can clear temporary faults.
  4. Consult the Boiler’s Manual: Refer to your boiler’s manual for specific troubleshooting steps related to the F27 error code. The manual may offer additional insights or procedures for addressing this fault.
  5. Professional Diagnosis and Repair: Due to the complexity of diagnosing and repairing issues related to flame detection and electrical components, it’s advisable to contact a Gas Safe registered engineer. A professional can accurately assess the boiler’s condition, perform detailed diagnostics, and undertake necessary repairs or adjustments.
  6. Regular Maintenance: Ensure your boiler receives regular maintenance by a qualified professional. Routine checks and servicing can help prevent issues like the F27 fault by keeping the boiler and its components clean, properly aligned, and in good working order.


The Vaillant F27 error code signifies a serious issue related to false flame detection, requiring immediate attention to ensure the boiler operates safely and efficiently. While some preliminary checks and cleaning can be done by the homeowner, most solutions will necessitate professional intervention. Regular servicing and maintenance are crucial in preventing such faults and maintaining the optimal performance of your Vaillant boiler.