Your boiler has lost communication with its external controls or is stuck in an internal testing phase, meaning it cannot start the heating cycle.

Temporary fault code (Refer to section 7.10)

What causes this fault?

This fault occurs when the boiler's main control board loses the electronic signal from the external timer or room thermostat, causing a break in communication. It can also happen if the boiler becomes stuck in an internal calibration mode after a power cut or a system reset. Essentially, the 'brain' of the boiler is waiting for a command to start that it can no longer hear.