Your boiler is unable to control the flow of gas correctly to create a flame, meaning your heating and hot water will not work.

Stepper motor fault (gas valve)

What causes this fault?

This fault occurs when the boiler's internal computer is unable to communicate with the motor that controls the gas supply. The most common reason is that the motor on the gas valve has failed electrically or the internal mechanism has become stuck, preventing fuel from entering the burner. In some cases, it can also be triggered by a loose wiring connection or a malfunctioning control board that is sending incorrect signals.