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

On the Optimax range Ferroli define F07 precisely: the exhaust gas temperature has become higher than 95°C for two minutes. Read the range qualifier, because it is load-bearing — F07 means something else entirely on other Ferroli platforms, an air pressure switch fault on the i25 and i29 and a PCB parameter fault on the FERcondens, and this page describes only the Optimax version.

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.