Your boiler has lost the connection to the temperature sensor responsible for your hot water storage tank, meaning it cannot accurately monitor your hot water temperature.

NTC3 OPEN Storage heater probe not connected

What causes this fault?

This fault occurs when the boiler's control system fails to detect a steady flame after several attempts to light. The most common reasons are a buildup of carbon on the ignition parts, an inconsistent fuel supply, or a sensor that has become too dirty to 'see' the flame. It functions as a safety shutdown to ensure gas does not flow without being safely burned.