What does the Viessmann Vitodens 050-W E391 fault code mean?
The E391 fault code indicates a problem with the domestic hot water (DHW) sensor in the Viessmann Vitodens 050-W boiler. This typically means that the sensor is either faulty or not providing accurate readings, which can affect the boiler’s ability to heat water properly.
Common Causes
- Faulty DHW Sensor: The sensor may have failed due to wear and tear or manufacturing defects, 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’s control unit.
Can I fix it myself? (DIY)
It is advisable to call a Gas Safe Engineer to diagnose and repair this issue, as it involves electrical components and safety risks associated with gas appliances.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for replacing the DHW sensor is approximately £150 to £200, which includes the cost of the part and labour. This is based on the typical price of the sensor and the average hourly rate for a qualified engineer.