What does the Vaillant ecoTEC plus F31 fault code mean?
The F31 fault code on the Vaillant ecoTEC plus indicates a problem with the flame sensor, which is responsible for detecting whether a flame is present during operation. If the sensor fails or malfunctions, the boiler will not operate safely and will shut down to prevent any hazards.
Common Causes
- Dirty Flame Sensor: A buildup of soot or debris can prevent the sensor from accurately detecting the flame.
- Faulty Flame Sensor: The sensor itself may be defective or damaged, requiring replacement.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer to diagnose and repair the issue, as working with gas appliances can be dangerous and requires professional expertise.
Estimated Repair Cost (2026 UK Prices)
The estimated cost for repairing the F31 fault by replacing the flame sensor is approximately £120 to £180. This includes the cost of the part and labour, reflecting the typical pricing for a qualified engineer’s service.