What does the Vaillant F.85 fault code mean?

Your boiler has detected that two of its water temperature sensors appear to be mixed up, preventing it from safely monitoring the heating system.

How much does it cost to fix Vaillant error code F.85?

Typical repair cost for the Vaillant F.85 fault is £120-250 including labour.

Flow and return temperature sensors have been installed incorrectly (inverted)

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

7 signs repair isn't worth it anymore.

Break-even maths on monthly cover.

Realistic UK prices for a swap.