Vaillant F.67 Fault Code

What causes the Vaillant F.67 fault?

This fault occurs when the boiler's main control board receives an impossible electrical signal from the flame sensing system, often due to a permanent short circuit or a component failure. The most common reason is an internal electronic fault within the main circuit board itself, though damaged wiring or a degraded sensing probe can also trigger the error. Because the boiler cannot accurately detect if a flame is present, it shuts down immediately to prevent unsafe operation.