What does the Vaillant F.25 fault code mean?

Your boiler has detected a potential overheating issue and has safely shut itself down to prevent damage.

How much does it cost to fix Vaillant error code F.25?

Typical repair cost for the Vaillant F.25 fault is £150-300 including labour.

Interruption in the compact thermal module (flue gas temperature limiter or thermal fuse)

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

Work through these before the call-out.

Lockout fault with a reset-needed pattern.

Safety-critical — turn off, read this.