What does the Viessmann Vitodens 111-W F70 fault code mean?
The F70 fault code on the Viessmann Vitodens 111-W indicates a problem with the domestic hot water (DHW) flow rate. This typically means that the boiler is unable to detect a sufficient flow of water, which can affect the heating of water for taps and showers.
Common Causes
- Blocked DHW Flow Sensor: A blockage in the flow sensor can prevent accurate readings of the water flow rate.
- Low Water Pressure: Insufficient water pressure can lead to inadequate flow rates, triggering the fault code.
Can I fix it myself? (DIY)
If you are comfortable, check the water pressure and ensure it is within the recommended range (typically 1-1.5 bar). If the pressure is low, you can top it up using the filling loop. However, for any gas or electrical issues, it is crucial to call a Gas Safe Engineer.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for addressing the F70 fault could range from £150 to £300, depending on whether the flow sensor needs cleaning or replacement. A new flow sensor typically costs around £100, plus labour charges.