Viessmann [F.64] fault codewhat it means and how to fix it

F.64 has the wording of a fault and the behaviour of a note. The row reads "Normal operation; burner restarts — Flame loss during stabilisation or operating phase", and the difference from F.378, which uses the same cause text, is entirely in that first phrase. The burner lost its flame, the control unit relit it, heating carried on, and the event was logged so that the next engineer sees it under the "b.4" message history. Viessmann's measures are nevertheless the full flame-loss set — "Check gas supply (gas pressure and gas flow switch). Check balanced flue system for flue gas recirculation. Check ionisation electrode (replace if necessary). Check the distance of the electrode to the burner gauze assembly and its contamination level." — because the causes are the same as for the lockout; the boiler simply caught this one.

There is nothing for the householder to reset, and pressing the reset combination on a boiler that is running normally only interrupts it. What F.64 is useful for is warning. One occurrence in a winter is weather. A run of them in the history, or F.64 appearing on the display more than occasionally, is a burner working at the edge of its flame signal, and the next stage is the lockout row F.381 on a cold morning. The ionisation electrode is the part most often responsible and is replaced at a routine service; flue gas recirculation and gas pressure are the checks that go with it. Mention the code when booking the annual service so the contractor looks at the history rather than only at the boiler as it happens to be running that day.