Your boiler has detected an electrical fault with the internal sensor that monitors the temperature of the water leaving the unit, preventing it from heating up safely.

Short circuit on flow sensor

What causes this fault?

This fault occurs when the electrical connection inside the flow temperature sensor has failed, creating a short circuit that sends an incorrect signal to the boiler's control board. The most common reason is that the sensor's internal component has worn out over time or has been damaged by moisture, meaning the boiler can no longer safely monitor how hot the water is.