What does the Viessmann F4 fault code mean?

Your boiler has attempted to start, but it has failed to detect a flame, so it has safely shut itself down to prevent a gas buildup.

How much does it cost to fix Viessmann error code F4?

Typical repair cost for the Viessmann F4 fault is £150-350 including labour.

No flame signal is present

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

Lockout fault with a reset-needed pattern.

Older boilers — thermocouple, draught, gas supply.

Safety-critical — turn off, read this.