Your boiler’s internal flame sensor is dirty and can no longer see the fire, causing the system to shut down for safety.

Photocell filmed over (dirty)

What causes this fault?

This fault occurs when the photocell, which acts as the boiler's 'eye,' becomes coated in a thin layer of soot or oily film. Because the sensor can no longer detect the light from the flame, the boiler shuts down as a safety precaution to prevent unburnt fuel from building up. This is usually caused by natural wear over time or a slight change in the burner's combustion quality.