Viessmann [FA] fault codewhat it means and how to fix it

FA is the mirror of F9. The row reads "Burner in a fault state — Fan idle state not reached" on the B1HA/B1KA, B1HC/B1KC, 111-W B1LB and B1LD and the 050-W BPJD; the older WB1A, WB1B and WB1C editions word the same cause "Fan not at standstill". Between burner cycles, and before it starts a new one, the burner control unit expects the fan to have stopped and to read zero speed from the tacho signal. If the fan is still turning — or the control unit is being told it is — the start sequence cannot begin from a known state and the unit locks out. Viessmann's measures are "Check the fan, fan connecting cables and fan control. Press Reset."

A genuinely free-running fan that will not stop is unusual; the commoner reality behind FA is a tacho signal that is noisy or stuck, so the control unit sees speed where there is none, and that traces to the low-voltage fan lead and its plug or to the fan's own electronics. On the Vitotronic 200-W B2HB the row is widened to "Fan idle state or set speed not reached", which folds the F9 complaint into the same code. The householder's part is the single reset for the unit (rotary selector to RESET under two seconds on WB1B, WB1C and B1HA; "R" for two seconds on B1HC; Reset key on WB1A; MODE and OK on BPJD; reset button R on a Vitotronic unit), then the contractor if it returns. On the 2020-on numeric-table units the equivalent is F.72 (fan idle state not reached).