Vaillant F64 Fault Code ((new))

Air is a common cause. Most Vaillant pumps have a silver or black cap on the front. Unscrew it slightly (have a rag ready for a few drops of water). If air hisses out, release it until water trickles. Tighten the cap. Reset the boiler.

The most common (and expensive) solution for F64. vaillant f64 fault code

Seeing F64 on your Vaillant? Your boiler’s temperature sensor (NTC) is confused—shorted or sending bad data. Air is a common cause

Press the "-" and "i" buttons simultaneously to view the last 10 faults, which can confirm if F64 is a persistent issue. Replace NTC Sensors If air hisses out, release it until water trickles

The is defined by the manufacturer as: "Electronics fault – Safety time exceeded (water pressure switch)."

A qualified engineer can test sensor resistance (typically ~12k ohms at room temperature) and replace them if faulty. Replace the PCB