Your boiler is struggling to keep a steady flame when it is running at its lowest power setting, causing it to operate in a restricted safety mode.

Comfort safety mode flame loss at minimum load

What causes this fault?

This fault happens when the boiler's internal sensors can no longer detect a stable flame while the unit is ticking over at its lowest power. It is usually caused by a worn-out spark probe that can't 'see' the flame anymore, or a gas valve that is no longer delivering the precise, tiny amount of fuel needed for low-level operation.