Viessmann [F.357] fault codewhat it means and how to fix it

The numeric table has a family of gas-starvation rows. F.357 — "Burner in a fault state — Insufficient gas supply" — is on the 100-W B1HF/B1KF and B1HG/B1KG and the 111-W B1LF/B1LG (the B1GA and 050-W B0HA/B0KA tables omit it). F.353, on every unit, is the graceful version: "Shutdown with restart if demand exists — Insufficient gas supply, burner output reduced", meaning the boiler has throttled itself and will try again. F.467 is "Gas supply insufficient during calibration. Contaminated or insufficiently sized gas line", and F.383/F.384 are "Possible contamination of gas line". All are a burner that could not get the gas it asked for. F.357's measures are the most complete: "Check that the main gas valve and the gas shut-off valve are open. Test static gas pressure and gas flow pressure. Check that on-site gas line and gas flow switch are correctly sized." Then a note only an installer would write: if the building's pressure regulator leaks, pressure creeps up while the burner is idle and the gas flow switch may trip on restart. Then the coil resistance at the fuel valve (approx. 4 kΩ), the cable to the fan unit, the ignition electrode's insulation, and "Reset the appliance."

Two things the householder can do are in the operating instructions under "No fuel": with natural gas, "Open the gas shut-off valve. If necessary, check with your gas supply utility"; with LPG, "Check the fuel reserves and re-order if required." A prepayment meter out of credit, a supplier interruption or a gas valve nudged shut are the innocent causes and the only ones you can clear. Everything else — working pressure measured at the boiler under full load, a strainer in the gas solenoid valve blocked with debris from brazed pipework (F.467's note), a supply pipe too small for a 32 kW appliance — is Gas Safe work, and a gas-line contamination row should not be reset repeatedly in the hope it clears.