Your boiler is failing to light its pilot light or detect a steady flame, meaning it cannot start the heating process.

Ignition, pilot or flame proving fault.

What causes this fault?

This fault occurs when the boiler attempts to start up but cannot establish or maintain the small pilot flame required to ignite the main burner. The most common reason is a worn-out thermocouple that can no longer sense heat, or a pilot injector that has become blocked with dust and soot over time.