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 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. vaillant f64 fault code
Save this post for later! 🔧
✅ Faulty NTC thermistor (temperature sensor) ✅ Wiring issues between the sensor and the PCB ✅ (Less common) A defective main circuit board If your Vaillant boiler has locked out and
⚠️ Result: No heat. No hot water.