Vaillant Boiler F64 Fault Jun 2026

In simpler terms, the boiler's "brain" (the PCB) has detected an inconsistency or a failure in the signal it is receiving from the gas valve. The gas valve is responsible for opening and closing to allow gas into the burner. If the PCB cannot accurately control this valve—or if the valve reports back an incorrect position—the boiler will shut down as a safety precaution to prevent gas flow issues.

Try a reset and check the condensate pipe. If that doesn't clear it, call a heating engineer – do not ignore the fault or try to force the boiler to run, as an incorrect air/gas mix can be dangerous. vaillant boiler f64 fault