Your boiler is struggling to stay lit when it is running at its lowest power level, often causing it to shut down for safety.

No flame signal with low output

What causes this fault?

This fault occurs when the boiler's internal sensor can no longer detect a steady flame while the unit is operating at its quietest, most efficient setting. The most common reason is that the sensing probe has become dirty or worn out, though it can also be caused by the gas valve failing to deliver a consistent flow of fuel at low pressures.