What does the Viessmann Vitodens 111-W F40 fault code mean?
The F40 fault code on the Viessmann Vitodens 111-W indicates a malfunction with the domestic hot water (DHW) sensor. This issue can prevent the boiler from properly regulating water temperature, affecting hot water availability.
Common Causes
- Faulty DHW Sensor: The sensor may be damaged or malfunctioning, leading to incorrect temperature readings.
- Wiring Issues: Damaged or loose wiring connections to the DHW sensor can disrupt communication between the sensor and the boiler control unit.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer for this issue, as it involves electrical components and safety risks. Attempting to fix it yourself could lead to further damage or safety hazards.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for replacing a faulty DHW sensor on a Viessmann Vitodens 111-W is approximately £150 to £250. This includes the cost of the part and labour, as sensor replacements typically require professional installation.