Ferroli [F07] fault codewhat it means and how to fix it

Ferroli define F07 precisely: the exhaust gas temperature has exceeded 95°C for two minutes or more. As an F code it clears itself once the temperature falls back, which is why it can occur repeatedly without anyone noticing. The escalation is the part to pay attention to. Three F07 events within twenty-four hours are promoted to A04, a flue gas fault that is a permanent lockout. So an appliance that suddenly stops on A04 has almost always been quietly logging F07 for some time first. A condensing boiler is designed to send comparatively cool gas up the flue, because capturing that heat is the whole basis of its efficiency. Persistently hot flue gas means heat is not passing into the water where it belongs — usually because scale or sludge is coating the heat exchanger, or because circulation is too slow to carry heat away. It also matters for the flue itself: plastic flue systems are rated for normal condensing temperatures, and sustained overtemperature is outside what they are built for.