Viessmann [F.346] fault codewhat it means and how to fix it

Every numeric-table Vitodens regulates its own combustion. Viessmann's appendix describes it: the electronic combustion controller reads the ionisation current, which peaks at an air ratio of 1, and holds the burner between λ 1.2 and 1.5; to keep that reference true it "regularly carries out an automatic self-calibration, also after power failures", briefly running the burner to maximum ionisation current for about 20 seconds shortly after start. The calibration rows are what happens when that routine fails. F.346, "Ionisation current calibration error", is the summary fault — "Burner in a fault state", measures "Check the gas supply pressure. Check gas solenoid valve strainer on the inlet side for contamination. Check ionisation electrode for contamination. Check flue system. Remove flue gas recirculation if required. Check the condensate drain (condensate blockage). Reset the appliance." F.464 is the current too low during calibration, F.468 too high, F.372 repeated flame loss during calibration, F.377 the post-calibration stabilisation not met (check the gas type setting; HBMU if repeated) — all lockouts. F.374, F.375 and F.376 are the same routine failing at its preparation, execution or plausibility stages, and their system characteristic is "Burner restarts": messages, logged in the history, no reset needed.

The measures are nearly identical across the family because the causes are: an ionisation electrode with deposits on it, a loose plug, exhaust recirculating into the intake, condensate backed up into the heat cell, a gas solenoid valve strainer blocked with debris, or — F.468's and F.464's specific line — "a lot of dust in the ventilation air (e.g. from construction work)". Viessmann repeat their note that deposits on the electrodes indicate foreign bodies in the combustion air and tell the contractor to look at the installation room and flue for laundry detergents, cleaning agents, toiletries or a dusty air supply; and if the gauze assembly and electrode have been replaced, to clean the fan unit, gas/air channel and venturi extension too. The householder's part is the single arrow-key reset for a locked-out burner and nothing for a message. A boiler that cannot calibrate is a boiler whose combustion is unverified, which is why these are not codes to clear repeatedly; on the Vitotronic 200-W the same job is done by Lambda Pro and reported as EA and its E-series.