Viessmann [F.65] fault codewhat it means and how to fix it

Three rows in the numeric table say the burner tried to light and the ionisation electrode saw nothing. F.65 — "Burner in a fault state — Flame signal not present or insufficient at burner start" — is in the 100-W B1HF/B1KF and B1HG/B1KG tables and the 111-W B1LF/B1LG, but not in the B1GA or the 050-W B0HA/B0KA, whose tables carry only F.361 with the same words: "Flame signal is not present or insufficient at burner start." F.379, "Flame signal not present or insufficient", is on every unit and is the same failure without the qualifier. All three lock the burner out. The measures for F.65 are the long list: gas supply (pressure and gas flow switch), gas solenoid valve, condensate backup and the condensate drain, then the ionisation electrode and its cable, the ignition and its module, and the ignition electrode's distance, contamination and insulation, ending "Reset the appliance." F.361's measures are shorter and point at the electrode and its connections, with a note that "deposits on the electrodes indicate foreign bodies in the combustion air" — laundry detergents, cleaning agents, toiletries or a dusty air supply — which is Viessmann telling the contractor to look at the room the boiler is in, not just the boiler.

For the householder the operating instructions give the same short list they give for any flashing fault code with a burner that will not start: with natural gas, that the gas shut-off valve is open (and if necessary check with your gas supply utility); with LPG, that there is fuel; then "Reset the burner" once, by showing the fault number with the arrow keys and holding up and down together for about four seconds until the rotating bar appears. If the code recurs, notify the heating contractor and do not reset again — Viessmann's warning that unrectified faults can have life threatening consequences is printed beside that instruction. The electrode that proves the flame on these boilers is a wear part, and the condensate trap that backs up into the heat cell in a cold snap is the seasonal cause; both are in the row.