Viessmann [F.359] fault codewhat it means and how to fix it

F.359 — "Burner in a fault state — No ignition spark" — is the one no-flame row where the control unit knows exactly which stage failed. The HBMU heat management unit switches 230 V to the ignition module at the start of the ignition phase; the module steps that up to the spark across the ignition electrode; the ionisation electrode should then see a flame. When the unit can tell the spark itself never happened, it prints F.359 rather than the generic F.65 or F.361. Viessmann's measures follow the circuit in order: "Check whether the ignition electrode insulation is damaged. Check for a voltage of 230 V∼ at the ignition module during the ignition phase. If not, replace the HBMU heat management unit. If 230 V~ is present at the ignition module but there is still a fault, replace the ignition module. Check connection cables and leads from ignition module and ignition electrode. Reset the appliance."

A cracked ceramic on the ignition electrode is the most ordinary finding: the spark tracks to earth through the crack instead of jumping the gap, and the burner never sees gas lit. The ignition module is next, a sealed transformer that fails outright rather than gradually. The heat management unit is last and dearest, and Viessmann make the contractor prove the 230 V is absent before blaming it. None of this is householder work — the only user-facing action is the single arrow-key reset the operating instructions allow for any locked-out burner, and the instruction to notify the contractor if the fault recurs. Gas is released for the safety time on every attempt, so repeated resets are exactly what the "do not reset several times in quick succession" warning is written for.