What does the Viessmann Vitodens 100-W F90 fault code mean?
The F90 fault code on the Viessmann Vitodens 100-W indicates a problem with heat gain, suggesting that the boiler is not achieving the required temperature for efficient operation. This can lead to inadequate heating and hot water supply.
Common Causes
- Insufficient Water Flow: Blockages or restrictions in the heating system can prevent adequate water flow, affecting heat transfer.
- Faulty Temperature Sensors: Malfunctioning sensors may incorrectly report temperatures, leading to improper boiler operation.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer for any issues related to gas or electrical components. Attempting to fix these problems without proper training can be dangerous.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for resolving the F90 fault may range from £150 to £300, depending on whether the issue is related to sensor replacement or system flushing to restore water flow.