F64 — Vaillant

The gas valve controls the flow of gas into the burner. If this valve is sticking, jammed, or failing to open/close as instructed by the electronics, the boiler will detect a mismatch in the gas/air ratio and lock out.

In simple terms: the boiler thinks there’s a flame present ignition or after the burner should have stopped. f64 vaillant

Because this error deals with gas combustion and electronic components, attempting to repair it yourself can be dangerous and may void your warranty. However, there are a few safe steps you can take before calling an engineer: The gas valve controls the flow of gas into the burner

In rarer cases, the main circuit board itself is the problem. The PCB is the hub of all operations. If it sustains water damage (from a leak above it) or suffers an internal electrical short, it may generate false error codes like F64. Because this error deals with gas combustion and