What is the of your Vaillant boiler (e.g., ecoTEC Plus 831)? Did the error happen after a power cut or a storm ? How old is the boiler?
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. f64 vaillant
Since this code involves internal electronic components and electrical testing, it is generally considered a non-user-serviceable fault that requires a Gas Safe registered engineer. What Does F64 Actually Mean? What is the of your Vaillant boiler (e
If the sensors show , they are dead and need replacement. The gas valve controls the flow of gas into the burner
This is a very common cause. The ionisation electrode (or flame sensor) is responsible for detecting whether a flame is present. If this sensor is dirty, misaligned, or faulty, it sends incorrect data to the main board, triggering the F64 error.
The flow or return sensors are sending a signal that suggests a cross-connection.