Your boiler has detected a problem with the internal sensor that monitors water temperature or flow, meaning it cannot safely regulate how much it heats the water.

Flow sensor – fault sensor damaged

What causes this fault?

This fault occurs when the boiler's internal sensor, which monitors the temperature of the water leaving the unit, starts providing inaccurate readings or stops communicating entirely. The most common reason is that the sensor has suffered electrical failure or has become covered in debris, preventing it from safely measuring how hot the water is.