High Lockout
F.67 on Vaillant ecoTEC plus

Your boiler's electronic control board has detected a confusing signal from the flame sensor, causing the system to shut down for safety.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Flame detector input signal is outside the limits (0 or 5 V). Electronics defective

What causes this fault?

This fault occurs when the boiler's main control board receives an impossible or conflicting electrical signal from the flame sensing system. The most common reason is an internal electronic failure within the printed circuit board (PCB) itself or a total malfunction of the sensing electrode that monitors the burner.

Engineer required

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

Find a Gas Safe engineer
Search the official register →

Related fault codes

F.27View →F.28View →F.29View →

Related guides you might find useful

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →