Your boiler has lost its connection to the indoor thermostat sensor, meaning it can no longer adjust the heating based on the actual temperature inside your home.

Control mode without room influence - Room temperature sensor heating circuit A1 shorted out

What causes this fault?

This fault occurs when the communication link between your boiler and the indoor temperature sensor is broken. The most common cause is a physical failure of the sensor’s internal components or a loose connection in the wiring that tethers the sensor to the boiler’s main control board.