Your boiler is detecting an issue with the quality or frequency of the electricity coming from your mains supply, causing the system to shut down for safety.

Electrical supply not 50Hz. Correct the electrical supply

What causes this fault?

This fault occurs when the boiler's internal computer detects that the incoming electrical current is unstable or at the wrong frequency. Common reasons include a failing motherboard that can no longer read the power supply correctly, or external interference from heavy machinery and portable generators nearby. In some cases, a fault with the street-level power grid or local electrical work can cause the supply to fluctuate enough to trigger this safety shutdown.