Ferroli [A05] fault codewhat it means and how to fix it

A05 is the Ferroli fan fault, and the manual defines it precisely: the tachometer signal has been interrupted for one hour or longer. That one-hour qualifier is worth understanding, because it explains the relationship with F15, which is the temporary version of the same fault. A brief interruption produces an F15 that clears itself; an interruption that persists is promoted to A05, a permanent lockout. So an appliance that has been showing an intermittent F15 for weeks and has now locked out on A05 has not developed a new fault — it has finished developing the one it already had. The fan proves that combustion products can be cleared through the flue, and no condensing appliance will open its gas valve without that proof. Ferroli direct a check of the wiring as well as the fan itself, and that ordering is sensible: a tachometer signal can be lost to a corroded connector while the fan spins perfectly well.