Your boiler has detected an electrical issue with the part that controls how much gas is burned, causing the system to shut down for safety.

Current modulation alarm

What causes this fault?

This fault occurs when the boiler's main control board loses the ability to properly manage the flow of gas to the burner. It is typically caused by a failing electrical coil on the gas valve or a breakdown in the communication between the valve and the circuit board. Because the boiler cannot safely regulate the flame size, it shuts down to prevent damage or unsafe operation.