What does the Vaillant ecoTEC plus F42 fault code mean?
The F42 fault code on a Vaillant ecoTEC plus boiler indicates a malfunction with the modulation sensor, which is responsible for regulating the boiler’s output based on heating demand. This issue can lead to inefficient operation and may prevent the boiler from functioning correctly.
Common Causes
- Faulty Modulation Sensor: The sensor itself may be defective or damaged, leading to incorrect readings.
- Wiring Issues: Damaged or loose wiring connections to the modulation sensor can disrupt its functionality.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer for this issue, as it involves electrical components and gas safety regulations. Attempting to fix it yourself could pose safety risks.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for replacing a faulty modulation sensor on a Vaillant ecoTEC plus boiler is around £200 to £300. This includes parts and labour, as the sensor itself typically costs between £50 and £100, with the remainder covering the engineer’s time.