What does the Viessmann Vitodens 100-W F79 fault code mean?
The F79 fault code on the Viessmann Vitodens 100-W indicates a problem with the battery, which is essential for the operation of the boiler’s control system. This issue can prevent the boiler from functioning correctly, leading to heating and hot water supply interruptions.
Common Causes
- Battery Failure: The battery may have reached the end of its life and can no longer hold a charge.
- Loose Connections: There may be loose or corroded connections affecting the battery’s performance.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer to address this issue, as it involves electrical components that require professional handling for safety and compliance reasons.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for replacing the battery in a Viessmann Vitodens 100-W is around £150. This includes the cost of the battery and the labour required for installation by a qualified engineer.