Fault Code — Vaillant F64

This code points to an (specifically a short circuit or incorrect signal from the flow or return temperature sensor). While it might sound minor, an F64 can force your boiler into "safety mode," meaning you lose heating and hot water.

⚠️ Result: No heat. No hot water.

Seeing F64 on your Vaillant? Your boiler’s temperature sensor (NTC) is confused—shorted or sending bad data. vaillant f64 fault code

If your Vaillant boiler has locked out and is displaying the error code F64 , your heating system is alerting you to an issue with its temperature sensing circuit. Specifically, F64 indicates an NTC (Negative Temperature Coefficient) sensor short circuit or a signal outside the plausible range. This code points to an (specifically a short